The popping out issue was resolved or at least diagnosed. A revised shift rail was offered which helped the issue and at the time the issue was prevelant the new rear outputs were not.
I have Orion#100, it has been torn down several times and the wear/condition is unreal, like new. Back when we were solving the popping out issue shafts were scarce and IIRC we could not source that bushing. I went to Mudraks and found one that fit but was too long, Gary said it was a 60 bushing, it needed to be shortened, little time with dremmel and cut off disc had it all good. The bushing inside the high speed gear tends to wear in and hour glass pattern which when decelerating on compression it oscilates which walks the shift collar off the teeth.
A new shaft, new bushing solve this, sometimes both are needed, sometimes only one side. For example upon rebuildng mine this week due to a bolt falling inside case and killing a few gears we had to replace the mainshaft, bushing was fine, I was still using the og main shaft so it was time. FWIW spend time making sure the input gear, pto gear, & rear bearing all go onto and slide on the tranny output shaft, makes install much nicer experience.