Its a known issue with all CForce, UForce, and ZForce models.
Unfortunately, the factory has only come up with a final fix for the ATVs. There is no fix yet for the UTVs. I am supposed to be receiving 3 UTV kits at some point, but they aren't the final production fix-kit.
What I have been installing on my is an Air/Oil separator that HiSun uses on their 500 & 700 engines. It goes inbetween the crankcase and the air box. Basically you take the vent tube, cut it in half, and install this piece.
Which is the in and which is the out?
I believe it will function like this drawing but not sure you will be happy with draining the catch tube often. Maybe add a catch bottle on the end. Usually the 800s get oil in the air box from the crankcase vent because of one or both of these reasons. 1-There is excessive blow by due to ring wear or failure or 2- excessive vacuum on the airbox due to restricted intake port or dirty prefilter. Easy enough to check. Warm it up, pull the line off the box, run it up to about 3000rpm and if the line is blowing enough to see and feel, you have a ring problem. If not, then better check the prefilter or intake tube.