I just bought these 72 Buick GS 455 convertible with 42,xxx miles on it from a 82 year old friend I worked with for years. He retired in 99 and I finally got enough money to buy it. The only thing is it was sitting in the garage since 1989. Before the weather got crappy here in Ohio we got it fired up and it purrs like a kitten(very large kitten). Was hoping to ask so question? Like what weight oil would you guys recommend?