I called Castrol's tech line. They said the only change made to GC was to meet GF-4. Agree. Now if only the additive package changed, I still think this oil will show great numbers. It turns out that the PAO base oil is what made this oil good and NOT the additive package. So logically if that stays the same, I'd expect similar performance. This is my take on it. Now lets break down Mobil 1, the world's leading synthetic motor oil that commands 65% of the market.