I have my rear window out this week to fix some rust under the gasket. MB made a great car but they screwed up when they designed the body that holds the rear window. This is hard to explain but if you have had one out you will know what I am talking about. The channal that the gasket sits in collects water! MB didn't really give the water that gets behind the gasket a way to escape so it sits. The corners of the rear glass are the worst, thats why a lot of W126's have rust holes their. Also along the bottom of the lip two body parts are welded together. Open up your trunk and stick your finder up uner the rear window you will feel the seam. Rust gets in their and you really can't get it out. MB should have molded drains into the corners and center of the rear window. They could have drained the water right into the gutter the trunk gasket forms.

Their really isn't anything we can do to fix this, but if you plan on keeping your W126 for a awhile I would pull the rear window. The gasket costs $80 and the putty is $30. It isn't to big of a job and if you catch the rust early it is simple to fix.

So the W126 isn't perfect after all, just close.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Hattie,
The 123 is the same way. Some say you shouldn't use the sealant as the gasket should seal itself. The way I figure it MB never intended water to even get into that channel. On my 123 there is a small hole in the channel that would drain into the trunk, about 1/4" in diameter. Someone told me the hole was there to drain paint, like when the car was painted at the factory. That didn't make sense to me. I used the MB sealant to seal or glue the rubber gasket to the body right at the lip of the rubber seal. Its pretty difficult to get just enough to seal but not enough to have it squish out but it can be done. Make sure you seal the glass/rubber as well from the outside. The way I did mine no way is water going to get into the channel. It doesn't and hasn't and I do check the drain hole periodically to make sure. Hope this helps, RT

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When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

It is funny you should mention that hole, I was just reading my sercive CD and it said to make sure to block the paint drain holes! I filled mine in, I used a two part marine epoxy called Marine Tex to fill the holes and smooth them out. I like that stuff it gets real hard and sticks to metal real well.

I bought the putty (it was $30! ) hopefully the window will be going in tomarrow.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Hattie, you should take pictures for members to look at how you done this. Some would be interested, well o.k. just me!

Pull the rear window and do all that just because of rust? I intend to keep my 300SD for as long as I can, but this is overkill in my opinion.

Nothing man made is perfect!

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1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver

If you ignore the rust, it will continue to spread out onto the paint. The vehicle will look terrible and the trunk will begin to leak.

This will happen within a couple of years if the vehicle remains outdoors.

The cost of the repair then escalates dramatically at that point.

What would you do? Just drive it and ignore it?

Ok I am digital camra challanged but I will do my best to get a few pics before it goes back together.

braverichard actually this is a very simple job, getting the interior trim parts off takes longer than pulling the rear window. The rust will get bad fast if you just let it go eventually it won't be worth it to pay someone to fix it. I have seen a few 300SD's that had almost no metal left their! Unless you are a good welder you cannot fix that, paying a body shop would run into the thousands.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Yeah I may do that... just ignore it or sell it.

Well, I just feel like having to do all that just adds more to the ever increasing list of work that needs to be done on these cars as they age. They are cheap to own cars, but for them to be cheap to own a lot of your time has to be used. Don't get me wrong, I'm not trying to discourage anyone with the energy and time to do all that stuff.

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1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver

Isn't that the truth. This is one reason that I very much appreciate this forum. Without the support of Hattie and Carrameow and others, I would quickly tire of the never ending laundry list of items that need to be done.

The investment in time is no small consideration.

When someone finally says "enough" and purchases a two year old gasser, it is certainly understandable.

BTW, Old Navy just did exactly that ('05 Dodge Magnum!).

Hattie,
Thats interesting. I wonder what the advantages are to sealing the drain holes? Doesn't make a lot of sense considering if the gasket is good, no water should get in there. And if the gasket is bad then the water has a way out. Being a contractor and having done many roofing/water leak repairs I have found it is easier to direct water flow rather than make something "waterproof". Water has a knack of finding its way into anything. Its easier to control where it goes than seal it out completely. RT

__________________
When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

rwthomas1 I only found one drain hole, however another one might have turned into a rust hole. The one I found would not do much, it was in the inside lip and water would never get up their.

Well the rear window is back in, kind of a pita getting the trim into the gasket. Other than that we just wrapped string around gasket and lubed it up with soapy water. My dad then shot the sealant in around the gasket just like the CD says to. I am very happy with the way this repair went, the rust should not come back for many years if at all. Also after replacing every seal back their my trunk is dry! Finaly all I had to do is replace all of the seals!

Sorry no pics, my sisters digital camra is mia and she is at work.

Brian funny you should mention that I was just thinking about the long list of stuff I still need to do. But check one thing off the list.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200