I got a VH-65 4th axis on eBay a few weeks ago and thought I'd try to share my experience tearing it down and rebuilding it. I really couldn't find much info about rebuilding these - I guess most folks send them out. Since I'm a hobbyist, and not doing production work - I can suffer with a bit of wear and slop etc, so I was willing to sort of get what I got as far as bearings and the worm went. I ended up detailing it all here - Doov's Projects Just as a note, my machine was retrofitted with the 4th axis card, amp, air and wiring before I purchased it. I had no idea if it worked, so that was part of the excitement!. Turned out it worked fine.
Let me know if you find it useful and/or have comments.
--Thanks, David