Castrol emailed me all the PDS sheets for their oils. I can see that Castrol Syntec 0w-30 (US) is NOT GC. It's viscosity @100C is 10.0 and it is not A3 rated. Patman, I sent you the email from work today bc I thought maybe you could post them on here for everyone to see. (I don't want to login from work). They also say there 5w-30 and 10w-30 are 9.7 cSt and A3 rated which is impossible. There data sheets look as reliable as trying to find their oils.