I did pour in water, and it did come out of the tubes. Apparently the debris in the cowl floated on the water or was displaced by pouring in a large quantity at once. I poured a large number of buckets all over the car without finding any form of leak. This was frustrating since I since I planned a 4000mls the next week and driving for days in a fungus smelling car was not appealing. At that point I decided to remove the right seat and carpeting and went to the carwash (the closest to rain). When I discovered that some water was coming out of the floor heater vents I removed the heater ventilator and by putting ma hand in the ventilation system I found that the bowl under the air intake was wet. Then I removed the wipers and cows (in my case it took just 5 minutes). There was a lot of debris in the cow, and since the car was parked at the right side of the street some of it moved toward the draining tubes it I used a gentle spray of water. After 10 minutes the right tube was blocked and the water started to rise.

Removing the wipers may be hard if your afraid to break the small cover , I bent the underside open with bent long nose pliers an the just pulled it upward with quit some force. Since I live 10mls from a Mercedes junkyard I was not afraid to break it. I did this several times and it’s still not broken.

Lifting the rear lower seat pad an lifting as much of the carpeting as possible would be a good start to find out where it is coming from.

Thanks Rob. I also poured the water slowly and it still drained out of those tubes. Poured fast- same thing. It came gushing out. I guess I really need to remove that cowl panel and make sure that drain is clear. It is very frustrating, because I cannot get those wipers off. I suppose I could break them off.

I am planning on removing the rear seating soon to see if water is coming in there (rear glass). I suspect that even the rear window may be a culprit, because there is some starts of surface rust areas inside the upper trunk, below the rear window. Tomorrow I am going to replace my broken antenna seal to see if that stop that leak (if there is one). I KNOW I have a leaky right rear taillamp gasket. I have saw water seeping in there before, but what was strange is that at one point, there was water actually inside my trunk lid, sloshing around in the "frame channels" when I would open and close it. It finally evaporated.

Rust below the rear window is easy to explain. The warm air from the cabin enters the trunk through a channel in the deck below the window. There the water condensates on the cold metal in the trunk under the windows, this is highly corrosive.
On my car it was completely rusted trough, had to be fixed properly by a body shop, they welded new steel in the damaged spots. These leaks flooded the trunk but left the cabin dry.
Finding leaks is nearly always time consuming and frustrating. The only way to approach such a problem is to go all the way, remove all interior parts so that you can see the bare body and use a lot of water. And if that does not help drive it like that on a rainy day.

I once had an 280 (1975). In a vary cold winter day I had to brake hard and an large piece of ice came from under the passenger seat and landed on the carpet. After a long search I found this was caused by a tiny hole in the firewall.

As for the wiper, being defeated by a piece of plastic is not good, here I speak in my profession as a psychologist/human factor engineer. If your frustrated by this just get some good pliers that fits an just yank it up. If it goes its fine, if it breaks replace it or glue it back on. It’s just a plastic cover for the nut. It’s not worth getting upset about. I have broken a lot in my life, and, I have to admit that sometimes it gave great satisfaction.

OK. I finally did it! I removed the wipers and the cowl and cleaned out under the cowl. Turns out that it was a waste of time, because the drains were not clogged. In fact, both of them were free of being covered with debris. Now, there was some debris in there that I cleaned out, so it was not a total waste. There was even some loose dirt on the side near the air intake opening for the blower. I cleaned all of that out too. Then, I poured in a little washer fluid and wiped all around in there. I think part of that problem is that strip around the cowl on my car is in poor condition.

Now- about that wiper! The driver side was never a problem- it was the cover on the passenger side. It was very stubborn. Finally, after getting agitated, I just give it a sharp push and it came loose, but it cracked. The passenger wiper was also a pain to remove. Its a bit long and I had to pull it out and had to bend it a couple of times, but I think I got it back in shape. Putting the cowl back on was also tricky- I did not know that you had to get those little lips back under the glass. We learn new things everyday. Then- I poured water down the drains- and water flowed out of both- so now I know the water problem in the right rear floor is from there as previously suggested.

OK the mystery continues- the floor (right rear) is now not soaking with water, but still damp. I raised up the bottom of the seat (it was already loose) and it is NOT wet under there.

Earlier today, I also got to resealing my taillight seal. I removed it and it appeared to be OK, but it was loose in a couple of spots. I went ahead and put some 3M adhesive silicone on the seal and between it on the top only, because there is no way water can leak in from the bottom because of the design.

We sprayed ALL around the rear window, taillights, antenna grommet and then opened the trunk to check for leaks. NONE. I cannot see any water coming in now, but it was damp there before. Perhaps just from that condensation that Rob mentioned? Or perhaps the trouble the entire time was the antenna seal- which WAS leaking before.

I am slowly narrowing it down. I will check the under the rear passenger floor carpeting again in a couple of days (after this rainy weather coming up) and see if the water has subsided.

Still unsure about the sunroof drains. I also poured water around it, but never saw any water coming out of the drains under the rocker panel. Maybe that is my problem?

86, you haven't mentioned if you have checked your A/C condensate drains yet.

Very simple to check and repair if that is the problem.

You need to remove the carpeted panel under the glove box and then the carpet panel which runs along the trans tunnel.

You will see a thick black drain hose that comes out from the ventilation system and then runs to the bottom of the trans tunnel out under the car.

These things are apparently notoriuos for perishing around this age and they leak water into the footwell.

Even given you haven't used the A/C it is so easy to check it's just something else you could eliminate without too much drama.

Cheers

__________________
1988 W126 420 SE

beware of fundamentalists!

Thanks.

Yeah, it sounds easy enough to check that. You are right- I have not even used the A/C yet. Actually, I do not even know if it works or not.

Second thoughts, your drain hose may be on the drivers side, it's on the left hand side in mine.

Cheers

__________________
1988 W126 420 SE

beware of fundamentalists!

Well, if is it actually on the driver side, then is it safe to assume that this is not the problem since it is the passenger rear floor that is damp?

I guess so, I'm just not sure that they didn't reverse the drain and put it on your passenger side as well.

As I said, it's simple enough to pull the covers off and have a look.

__________________
1988 W126 420 SE

beware of fundamentalists!

OK - I have some good news! I think....

Seems as if my water problem in my right rear floor has stopped. Strange, but it seems like it stopped with I replaced my antenna seal. Strange though, considering that the antenna is on the driver side and the water was getting on the right rear floor. I suppose it was flowing over there somehow.

We have had several moderate rains since the replacement and the floor is DRY! I am hoping that was the problem. I am still having the leaky right rear taillight problem. I tried to reseal, but it was a no-go. I guess I am going to have to break down and buy a new seal, but I do not know if it is the lens to housing seal leaking, or the housing to car body leaking.

Thanks again for all of the replies. If any changes, I will report.

I thought the missing vapor barriers on my 350 were the cause of the leak on my car, but being greeted to gallons of water in the back seat footwell this morning debunked that theory...

I tested with a hose, and the leak is from the windshield cowel drain on the driver's side. I cleaned up the lill compost heap under the plastic cover, but that didn't solve the problem. Water flows nicely down the drain hole, but some of it ends up in the car, dripping down by the parking brake lever. From there it runs down the floor mat, into the back seat.

How do I go about fixing this? Is there a rubber tube that should attach to that drain hole or something? I'm also quite worried about rust now.... the bolts for the front seat track are all rusty

-Jason

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

The edge between the plastic drain tube and metal leaks. I used some aluminum flashing to build that out so the water runs right into the tubes, and glued it in place with some Marine Tex. .

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

So how did you get to the tube? I looked up in the dash and couldn't see it, but I didn't take the knee bar cover off.

-J

WOW what an old thread. I had forgot about it!

BTW - after I replaced that antenna seal ($3.00), not one drop of water came into the car again! Hard to believe a worn antenna seal on a 85 380SE would allow water to go into the rear passenger floor!