My 73 Challenger was sort of the same way. It was black and oozed all over everything. It wasn't extremely hard though once you got past the outer crust. It was factory, on my car anyway. I know it wasn't the tape that people use to reinstall the glass.

I poked a hole through the caulking and inserted some braided metal wire through the hole. My dad and I sawed all the way around the glass.