In my quest to find which oil I was going to switch to and start using, I have been asking everyone I know what they are running. One of my friends running a GSXR 600 showed me the oil he is using. It was Castrol Syntec synthetic blend(part synthetic) 10W-40 motor oil. It was not motorcycle specific anywhere stated on the bottle. Does this matter at all? I assumed it was not a big deal, and didn't want to tell the guy to switch if he likes it. But I figured I would ask here for opinions that maybe I could pass along to him. P.S. My new choice is Amsoil full synthetic, however it is becoming super aggravating trying to find the stuff. Its not available anywhere in my area(Naperville,IL) and I called 2 different "Dealers" for Amsoil in my area, and one never called back. The other told me just order it from Amsoils website. Is that the only way to get their oil? Thanks for your inputs.