Klatu. Barrada, Nicto. LOL..
Anyways, back to your question(s). I have an 8520 and have seen a couple folks "rebuild" the head. The bearings are available and I don't remember them being totally outrageous in price.
No more than you'd expect to pay for a precision bearing. The hard parts are the fine feed gears. They aren't available new to my knowledge, but I think Boston gear has some acceptable substitutes.
There was a couple "pages" around the net of folks doing the overhaul / service, if you need to see them I can try to hunt them down again. Lastly, if you can find a 8520 and can work it out, grab hold of it!
I thoroughly enjoy working with mine and it was expensive for my pockets, but once you get past the price it is worth every cent! It's very capable for it's size.