Carpet Backing
 

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.