79 240D - Bad rear window seal and flooding trunk

[Stugist]

I'm new to the forums here, and I wanted to see if I can get my leaky trunk fixed.
Recently, I bought a very decent 1979 240D, but unfortunately the rear window seal is going bad. Nothing leaks into the cabin (I don't think, I haven't pulled the back seats to check), but there was a pool of water in the trunk when I bought it. It only filled the side pockets on either side of the spare wheel/jack well, plus underneath it (from what I can tell). I've since drained the water from the sides and had the car covered. What do I do about the water under the spare tire compartment? Someone suggested drilling a hole on each side for water to drain.

Also, any suggestions for getting a new window seal? Thanks!

I'm relatively new to cars, and I figured this would be a great learning opportunity.

[bipolardave]

I can't speak for the W123, but the rear seal in my W115 is a bear. So much so that the local glass installer gave up for fear of breaking the glass.

As I understand it, the proper technique is to pull the glass and seal from the inside of the vehicle using a roper or wire as opposed to only pushing from the outside.

There are several company's that make the seal and some are probably better than others, so do a search for reviews and possibly part #s. At a guess, I'd say it's a $100 part. My new seal came with the car, so I know nothing about it.

My W115 has several holes already in the trunk, including one in the spare tire well. I'm curious as to why yours doesn't. But you should be able to drill some without any problems. Just be double check to ensure there's nothing beneath that you might damage.

[Phillytwotank]

There are drain holes in the floor of the trunk on each side and in the bottom of the tire well. Sides will be covered with the internal plastic lining but you can poke through from the bottom to clear ant debris that might be preventing them from draining properly. You should be able to see the tire well drain fully with the tire out.

How bad is the rear window seal? flow-able silicone from the auto parts did the trick to seal my old leaky seal.

Post a Pic of the seal.

Finding a competent glass shop to to the job might be tough but at least the seal and the glass is pretty widely available for the 123 sedan.

[rocky raccoon]

I think you will find that there is more wrong than the seal. On my coupe, I found that the seal seat (channel) had rusted clear through in several places. It was fixable at a cost of $350 plus $100 for a glass shop to R&R the rear window.

A new seal was almost $200 but that was for the coupe. A sedan seal should be much less since the coupe seal has a much smaller population.

Please let us know what transpires. BTW a silicone injection (so to speak) may/may not work in the short term but is far from a permanent fix. In my case, the cost of doing it right was well worth it as there is no rust anywhere else and the old 300cd is my daily ride.

[sleepstar]

clean out ALL the channels around the trunk lid, and clean out the drains. it may not be leaking in through the seal.. i think you'd notice it in the cabin if it was. check for dampness under the rear passenger carpet..its the lowest point in the cabin and water pools there. i had a lot of water in my trunk and it was fixed by simply cleaning out ALL the channels and drains

[Left Coast]

In my experience with trunk leaks, there is equal probability that the rear window seal, trunk seal, or tail light seals are responsible. It could even be coming from all three places at once. The only other possibility on a '79 W123 is the antenna mounting gasket, which would only leave water on the driver's side. I wouldn't rush to diagnose without doing some careful investigating.

Dry out the inside of the trunk. As previously mentioned, make sure that the trunk seal channel is clean. Then give the entire inside of the trunk a light dusting with cornstarch or baby powder and let it sit through a couple of good rains. The cornstarch will reveal the paths of all leaks very clearly, and by observing them you can determine how to deal with the problem.

I have replaced the rear window seals on two vehicles, and one windshield seal. I did them all by the book, except that I substituted 3M bedding sealant for the MB stuff. My results with aftermarket seals were mixed. One was a poor fit that required much additional sealant to get it water tight. I doubt that it will last for more than a couple of years. One held for five years and had its life extended by two more with some flowable silicon in the glass channel, but needs to be replaced this year. The only one that went in without a lot of foul language and wasted time was a genuine MB part. It is also the only one of the three that didn't leak at all after installation. From what I have read on this, and other MB forums, a good number of aftermarket seals are problematic, while there are very few complaints about the genuine parts.

[Stugist]

Well it's a beautiful day out so I'll get a picture of the seal when I get home from work.

I pulled the rear seats yesterday to check for water damage. Bottom cushion is nearly perfect, only a bit of rust on the frame corner. When I pulled the back cushion, though, almost the entire cushion support frame is covered in rust. The inside just looks mangled. Leather's spotless though, haha. I still have to clean the black liner and pull that to check under it for damage. While I'm at it I'll check under the rear passenger carpet.

I've seen pictures of the seal channels complete annihilated by rust...not pretty.

[Pooka]

From what I have seen on 123 and 114/115 cars the culprit is almost always the taillight seals.

A quick fix is to remove the taillight and then remove the seals. Coat the seals with a lithium grease and reinstall. Unless you have a seal that has cracked this usually works.

This will take a lot more grease than you might think as dried out rubber really soaks it up. I would start with two cans of spray grease and be sure to coat both sides until they are wet. If you don't use all the grease on your seals then use it on the door seals. It works well there, too.