this bearings for avid are very durable:
http://www.avidrc.com/?action=item&i...=1&prevstart=0
a buck a piece!
follow his clutch bearing prep.:
http://www.avidrc.com/?action=support#life
they will last at least a gallon. they will last longer than that for sure, but if you want to be safe, you can replace them every gallon or 2.