Saito is pretty explicit about not using Castor oil in their engines; something about varnishing up those little valve-thingies, I believe. My Saito .40 is very reliable with Pat Johnston's C/L mods. 1-flip starts, and turns an 11-7 APC at 9800. I launch at 9000, and it's like a tractor engine.
Edit: I should have added that I use only Powermaster YS 20/20 fuel, and the tank uses standard venting, not uniflow.