Soft alloy spacers are always the weak link. If you start with a good steel spacer, good seals, and good beraings, you should never have to change bearings again as long as you pull the wheels every few rides and clean the seals, and also keep the pressure washer away. The seals will also last because the dirt will stay outside and not get under the sealing lips wearing them away fast. My friends son is still running around on my old '03 with the original wheel bearings. I have SS spacers made as part of new bike setup. Also, pack the gap between the bearing and seal with a good marine grease like Castrol Pyroplex Blue, this will efectively waterproof the bearing if he seal is worn.