Sometimes bearings wear out for no direct cause. I would suggest the thrust washers, bushings and bearing all be replaced in the gear train.
Check clearances and check for wear. Look at the planetary pinion pins for movement forward and backwards. When the pins move , they wear into the thrust washer
Some people are like Slinkies... Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs.