Bearing life seems to be dependent on manufacturer of bearing. Bearings and mechanics of water aerator windmills is quite different than old fashioned water pumping windmills. Some of the bearings in 2yr old Koenders and Superior mills were failing after 12-18 months due to cheaply made or a bad batch of bearings. I think current mfgd mills are using different bearings. Water condensate frozen airlines causes a high percentage of damage due to air not escaping. Common sense and a little fore thought can prevent some problems.
