Check for sumping after a ride and carefully remove the pipe plug on the right (brake) side of the crank case. If more than 6 ounces drains out, the motor is sumping. The fix is replacing the o-ring at between the oil pump scavenge spigot and the crank case. Years ago, I started using an additional o-ring behind the scavenge port o-ring to insure a tight fit at the scavenge port. I use the o-ring that goes on the oil pan drain plug for that purpose PN 11105. Also align the oil pump when putting things back together and carefully tighten the pipe plug. Apply some thread sealant and just snug it up; no need to go "gorilla" on it.

 

Classic sumping, Ed and djl nailed it.
Scott