Poor fuel, ( there is actually a service bulletin from brp that explains how poor fuel was causing unburnt fuel to enter crankcase and in some cases actually causing oil to overflow out of dip stick!) we should be running reg not high octane as high octane and octane boosters actually cause fuel to not ignite as easily. That is why high compression or forced induction systems require high octane it's so fuel does Not ignite (detonate)from heigh temps and pressure in cylinder, before spark. So basically there is NO benefit from high octane or octane boosters unless you are running extreme compression or forced induction.
Also weak feel pump, or any condition where bike is stumbling and running really rough, can cause fuel to contaminate oil, as any un burnt fuel can find its way past rings ( even on a healthy motor!) also running bike in cold conditions for short periods without proper warm up time is also mentioned in that bulletin as a cause of fuel contaminating oil. Motor needs heat and pressure to seal up properly so until bike is warm rings, valves etc won't be properly sealed. Even timing being off, or improper valve adjustments could cause fuel in oil.
