Best to replace all the bearings and seals while the unit is apart and you will not have to do it again in the near future. Original brands are available from after-market resources for big savings on the parts. In any case, if you slightly pinch the bearing in a vice and rotate the axle, if bad, you will feel the bad spots in the bearing as the axle turns. Pinching the bearing in the vice simulates a load for testing the bearing when the axel is turned.