Hmmm, according to this (and other things I've read) even "100% Synthetic" doesn't mean full PAO base stock. Interesting reading: Finally we have the truth about synthetic oil. | Habot Marketing (Pty) LtdMobil 1 is Full synthetic just like the Penzoil is Full synthetic, what does that mean? It's a marketing term because neither one is 100% synthetic or don't you think they would say that. The API says that any oil that is over 67% synthetic can be called Full synthetic, but only in the US. Isn't marketing great. Get a 100% synthetic oil like Royal Purple, Amzoil, Red Line or Bel-Ray and find a decent small shop or do it your self. GM dealers have smashed more fenders than anyone.