Mine were shot too, but not due to dirt or grease breaking down. The race developed a knotchy surface early on, maybe they got loose, or maybe there was dirt in there early on. Later the grease was clean but the notchiness got really annoying so I replaced the lower bearing. A real bitch to do - hope I don't have to do it again.
I borrowed the right tool, a flared, split tube, to drive out the races, and the lower inner race is much easier to drive off the pivot tube if you just go ahead and rip off the cage/rollers. There's a nice lip there to drive on with a chisel instead of destroying the seal trying to pry it off.
