Frank and John,
Isn't one of the things that has affected motor oil formulations emissions requirements. For example I thought I read somewhere that diesels are now equipped with cats and the old oil formulations damaged the cats so a new diesel motor oil formulation was required. If that is so maybe the older oils are actually better for gas engines with flat tappet camshafts. That's an interesting question to me because I'm no expert on the subject, just an interested amateur.
Ray W
