I have an RX-8 Revolution. There are two oil ring seals on every sides of the rotors. Inside these seals are O-rings. Do you know that are these O-rings made of rubber or cast iron? I\'m courius because if these are made of cast iron, than the "true synth-synth-mineral oil" question is answered: No matter. But if these are made of rubber, than I don\'t know.
I can buy Mobil oils cheaply and those are greats so I use Mobil-1. My "problem" is that here are only 0w-30 or 0w-40, (isn\'t 5w Mobil-1 oil which is close to the 30 grade), so these are true synthetic. Now I use 0w-30, but I don\'t know it\'s affect on these O-rings, if thats are rubber.
I know there is Mobil Synth-S 5w-40, but I think Mobil-1 is better.