I recall having a layer of caulk like/adhesive "stuff" between the mating surface of the fender to the inner fender. It appeared to be a very thin bead of caulk that was "squished" when the fender was bolted down and became very hard/brittle after it set up. I remember it on two '59s but not on the '61 I have now. None of the cars appeared to have ever been disassembled prior to me. I didn't put anything back except, as Marv says, a good coat of paint. It was not thick enough to affect fitting, but was very hard to sand off, short of using a disk sander. It was only along the top, flat surface of the inner fender. If you are talking about the area where the fender bolts into the side of the front apron, then...what Randall and Marv said.