Mobil 1 does NOT list 5W-30 Mobil 1 Extended Performance Oil as meeting the "GM Corvette Spec" (GM 4718M) anywhere on the bottle or on the website. I emailed Mobil 1 about this and they replied that it DOES meet the GM 4718M, and that I can use it. BUT, I am cautious, why wouldn't they list this on the bottle or website? Could it be that the "extra additives" detract from it meeting this spec? Your opinions wanted.