Originally Posted by FBinNY

Some used cartridge (sealed) bearings, and are basically non-serviceable except for adjustment. Many are still classic cup/cone types like you had before, and should be cleaned and repacked once in a while depending on mileage and riding conditions.

IMO= just about all can benefi from an improvised boot to keep dirt and rain out of the lower bearing. The upper seems to hold up well without extra help.