Bipeman, the paperwork I got for mine says 5% oil. But I don't think it's from OPS but rather from the distributor, Shamrock Imports. Also, I have a engine review from "Radio Control Models & Electronics" (an old magazine review) where they also specified using 95% methanol and 5% castor. Because of the needle bearings at both ends of the piston rod they are not supposed to need a lot of oil. More oil than necessary is said to make the carb adjustments more critical.

Maybe your crank damage is from a combination of overrevving, and using nitro? You are not supposed to use nitro in these. Where is the damage, on the crank pin or the shaft?

I have heard that these are even being converted to gasoline/ignition running on 40:1 gas/oil.