What type of sealant did GM use on the firewall on my 66ss? I am going to paint it and this stuff is getting old. I have found that 3M product makes this stuff. Its called Ultra pro, part #08655. Is this like the factory sealant? Can I buy this at places like Home Depot or Menards under a different name or title. I was told that I could save a few dollars on the same basic thing at a home center type store.

You won't find anything like ultrapro anywhere but an auto paint outlet. It is excellent stuff, and well worth what you pay for it. I think you can't beat anything that 3M makes. They also have a urethane type sealer that is a step above the ultrapro. It is basically the same stuff the new cars use to hold the glass in. Comes in black and white.