If it passed a leak test and you have got the jetting sorted, and have done 3 or more heat cycles, take it for a ride.
Some times on assembly one can use a little too much oil and it will pool in the crankcase.
On idle and light throttle openings, like you do when you heat cycle, the oil does not purge like when riding under load.
If that is not tranny oil and the pipe is leak free you may just find the oily problem will go away after a bit of a ride.