Like the other guys have said: cardboard. It looks like a gigantic oil spot. Not exactly reassuring. The newer paint job might not mean a bad thing but it's something to check on. And trying to sell your Cutlass before he sells his Buick is waaayyyy too risky. If I were you I'd try to work out a trade instead. I know you're into the turbo Buicks, but you better make sure this black cat is a winner before you ditch the clean Cutlass.