while I was troubleshooting/fixing the cause of the leak in my 1984 300D, I discovered the foam backing for the float matts was like black sand. I can brush it of like sand, I was using some of that spray on stop leak. I bought two cans thinking I might need to do both driver and passenger side.
I had a whole can left over, so I decided to brushed of the remaining foam from the back of the carpet and sprayed it with the "Leak Stopper" Rubber flexx sealant I got from Loews.

This stuff is great for carpet backing, I thought I share.

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1984 300D, 1972 LT1 Corvette, 2014 Artic White 3LT/Z51 C7, 2013 650i Convertible BMW, 1994 Kawasaki Vulcan, 1992 Yamaha Seca II and 1996 Dodge Ram 2500.