I do find it amusing that some of those who bash Castrol for changing the definition of synthetic, saying that going with grp III basestock cheapens the product, still hold up Mobil 1 as a top tier SYNTHETIC oil, even though XM started adding significant amounts of GRP III as well. You can't have it both ways. If GRP III is OK for XM to use, then IT'S OK FOR OTHER OILS SUCH AS CASTROL!
GRP III oils give excellent results. That should be all that matters.
GRP III oils give excellent results. That should be all that matters.