I haven’t done such procedure, yet. But from what I know, the bearings on the crankshaft sit quite well in the housings of gearbox. In order to disassemble the gearbox, it is necessary to be attentive to this moment and influence housing either with heat or mechanically (but be very genteel). Hope it helps.
this issue is a regular problem with MXU 450. one time in the while you should replace the starter and gear because the teeth is not strong enough to does longer then 2 -4 year. I have also tried to find alternative starter but Kymco did all that their starter has unic specifications.