Leather was only available on the top luxury models (Cutlass Brougham, Regal Limited, etc) when it was available. It is likely that if it has survived all these years and is not stiff as a board, it is vinyl, not leather. GM has never used good leather anyways, so it is just as well. If you really want vinyl, try to get a product called "MB Tex". It is the OE vinyl used by Mercedes Benz in the 70's and 80's. It is not cheap, but it will outlast anything else. Mercedes also used an awesome leather too that is probably 2x as thick as the stuff GM used. Again, not cheap, but you won't have to do it again unless you neglect it.
