What is that hardened puttylike stuff on the firewall of my 66ss? It is cracked and there is some light rust in some areas near it. I am going to paint the firewall and I want to get most of it off. How do I get it off? And how do I apply new sealer and make it look good? And finally, where can I buy this sealer?
Thanks in advance...

I dug some stuff off my 70 Malibu. You can get it at an Auto paint shop. 3M body sealer, brushable. Or as a roll of the stuff. I think 1pt was 23.00. I tried some other stuff called "RustFre", it is the black stuff they spray on for rust proofing new cars. It was 14.00 a gallon, but I think I shoulda got the 3M.
DG

Napa sells the stuff in a tube, under the Napa brand name, called Seam Sealer. It comes in a caulk tube. Dig out the old stuff, clean it up with a wire brush, spread this stuff on out of the tube onto the seam, and follow it with a semi-stiff paint brush, like the one you didn't quite clean good enough, though you thought you did. It'll look almost like the factory did it, although you still have to paint over it, as it comes in only white or grey. But, it stays pliable, and keeps water out.