I changed right front and left rear wheels bearings a few weeks ago and was able to re-pack them with some high-temp race grease. Here's a little write-up on what I did. I took the bearings apart, cleaned out all the grease, and then re-greased them with some Neo Synthetic.

Front bearing: The front bearing does come apart, but you have to bang on the inner piece pretty good to get it to come out. There's little tabs in the ball cage that lock the inner piece in place and you have to bang it out of those tabs. I did not remove the grease seal on the one side, but you could probably do it if you wanted. I didn't feel like dealing with the hassle of getting it back in. I was able to clean the bearings on that side while they were still in the housing. You just have to move the bearings around a little bit. The front bearings have the balls locked into the cages so don't try to remove the balls. Just remove the entire assembly. Re-assembly is pretty easy, just put the ball cage back in and tap the inner pieces back in.

Rear bearing: The rear comes apart easier than the front. A little tap will get the inner piece to come out. The balls in the rear do pop out so I took them out to clean them. I was able to clean everything without removing the grease seals, but when I went to put the inner piece back in it wouldn't seat correctly. The inner piece seats into the grease seal and I couldn't get it to seat all the way with the grease seal in the housing. I wound up taking the grease seal out, putting the inner piece into the grease seal, and then tapping the inner piece and grease seal as a unit back into the bearing housing. That was the only way I could get the inner piece to seat all the way and not leave a gap where dirt could get into the bearing.

Here's some pics:

Magic goo


Front bearing disassembled.


Front bearing balls and cage.


Front bearing inner piece. Note the grove where the tabs in the ball cage hold the inner piece.


Apparently I can only have 4 images in a post so I'll put the other pics in a separate post.