I have read that stock spurs should be one of the first thing to replace since they are made from some glued powder, but so far only teeth iv lost are in back diff ring gear - waiting for replacement atm 🙂
Have you tried removing motor and running it to see if the shaft is actually bent and wobles while spinning? Also - if shaft is fine and you are still loosing teeth from pinion or spur gears my educated guess would be to inspect the cush drive - its designed to save those gears.