Your velocity stack shuld prevent a lot of "spit back" which could be your one of our sources of extra oil all over the place. A lot of people do not realize there is an 0-ring between the velocity stack and the carb, need to close up that space. Other folks have resorted to using air filters that also prevent spit back. And finally, I figure you have an tube extension on the crankcase vent. Several inches of tubing firmly fixed so the tube does not flop all over the place. I have seen guys have up to 10 inches on that vent and it is strapped to the landing gear with a tie wrap.

Cheers,

Chip