The input shaft on the T-50 gearbox only has one bearing on the shaft...

The pilot bearing is there to locate the end of the input shaft and prevent the
shaft from "flopping around" when the clutch is disengaged. The bearing is only
working when the clutch is disengaged. At all other times the input shaft and
crankshaft rotate at the same speed.
FWD versions don't use a pilot bearing, and it is not unusual for the bearing to
be missed out on RWD conversions. However, while not have the bearing can
cause some clutch vibration and noise, I have no knowledge of it destroying
gearboxes. Just tap the bearing in until it bottoms out, re-assemble, and you
should be fine. Make sure the bearing is a sliding fit on the shaft beforehand
Cheers... jondee86