I just went through this ordeal. I used a scotch brite pad and 100% acetone. Used a paper towel to wipe up and then a piece of masking tape to get the stragglers. When I pulled up the floor soundproofing I used a heat gun and gasket scrapper and then hit it with a large cup wire brush on an angle grinder. I planned to paint afterwards. But it still left a lot of residue and I had to go back to scotch brite and acetone to get the rest up.

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1978 Mercedes 240D
1981 Mercedes 240D
1982 Mercedes 240D