I had same problem with my 2012 E350 4matic. After clearing sunroof drain holes,I still had the problem. It turned out to be the windshield sealant right along the top edge of glass. I masked off top edge of windshield glass and edge of car roof and tooled in Permatex Windshield Silicone Sealant. It is a more fluid,liquidy version of silicone. It flows into crevises. No more problems the past 5 years.
I use and recommend Permatex 09128 for brakes. It can take the heat and it's made for this application.
At some point the valve cover gaskets leaked (it might be a common problem) which I fixed myself with a tube of Permatex.
you can peel back the outer \"lip\" on the gasket type seal and use flowable silicone windshield seal (permatex makes it..). peel back the outer lip starting at the top and start to apply the silicone toward the sides and the bottom.. be very careful because this crap flows everywhere and is nasty.. so use it sparingly. i have used it on quite a few cars with great success. my wife's 81 leaked on the sides of the seal and i used the permatex product, and no more leak after that.
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The Permatex brand is registered in USA. Official website: https://www.permatex.com/ .
In March 2026, PartReview recorded 4 reviews across 3 parts by Permatex. Average rating — 4.7 out of 5.
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