How do I replace the Shaft Bearing Set?
Remove the brushes. With the washer unplugged and lying on its side remove the screws or bolts on the bottom of the washer. Pull the bottom plate away from the washer exposing the gears, spacer, bearings and bushings.
2) Replacing the Bearings
Pic of upper and lower sitting flush

3) Rebuilding the base of the washer
Once all pieces have been placed back in there correct spot place the lower Plate over the gears and spacers and push together. It is helpful if the washer is completely vertical upside down. This keeps the pieces straight and easier to line up all the parts with the holes in the plate. Once the bottom plate is seated properly replace the Plate Screw Assembly being sure to use Spacers. Hand tighten, replace brushes, place in sink and begin regular use.
Cause or how do I avoid this problem from repeating?
Using a quality recommended low foam bar glass cleaner is the most effective way to avoid wear and get the best results. Adding a mineral solvent to your first tank in hard water areas will also extend wear.
Using the wrong Brushes for your glassware, pushing down hard on the brushes and washing pitchers on the washer is detrimental to your machine and will cause premature wear.