[Alan Anderson]

If the bearings want to fall out, they've probably been put in from the wrong side.

If the gearbox is extremely noisy, it's possible that one of the gears has been installed upside down and the gear is not being held away from the bearing by the tiny "bump" around the center hole.

If the gear tooth sensor mounting holes either put the sensor too far out from the gear or require long standoffs to reach the gear, it sounds like the lexan plate might be flipped 180 degrees from its proper orientation.