Is Castrol Syntec commenly called "GC" on this forum? I thought "GC" was originally German Castrol that was green in color. I assumed that German Castrol was brought in from Germany/Europe, but I don't really know. I ran some dealer Castrol in my 2004 Tundra and then switched to Mobil 1 before I sold it. I'm currently running Pennzoil Platinum in my 2004 Sequoia and am considering options to improve fuel mileage as my wife has a longer commute as of last week and any savings would be nice. I'm currently running 5w-30, but might consider going to 0w-30 if I thought it might help. With 75,000+ miles on the clock I'm a little concerned by Mobil 1 finding some leak paths since I have had it leak out of engines that nothing else did. Mostly looking for some GC clarification.