I have a 1980 Mercedes Benz 450SL that I am restoring. The paint is original and is in pretty good shape and I believe that it is lacquer. If I apply some lacquer thinner to a rag and rub it on the body, I do get the color to come off on to the rag. Can I apply a urtheane primer on top of the prepared lacquer or, do I have to strip the car down to bare metal? I plan on using Sherman Williams Ultra 7000 base coat and clear coat.