The bearings are going to fail, its just a matter of time. They are sealed and cannot be greased either. You can remove the outer seals and the bearing race seal as well to shove in some grease, but you can't replace the race seal once you have done this. Basically the bearing is very susceptable to moisture and trash then. When you replace the bearings there are ways to drill the carrrier, install a zerx fitting and get some grease to the bearings, but you have to remove the inner race seal and take a chance of blowing the outer race seals everytime you pump in the grease. I did this to my 300.
The best thing to do is check your bearings everytime you clean it good. Jack it up and check for play. You should be able to catch it before the bearings have a chance to seize, however, freak things do happen. It just happened to a friend of mine with new bearings!
Honda, Best On Earth
2000 400EX, 1996 300EX and a 1997 LT80 - each with a bunch of custom schtuff on'em!
2001 CR250
2002 KDX220