Yes, I did service them myself. Big cameras, big parts, not very hard to work on if you know what you're doing...which I not always did...:0
In total, I did rebuild 3 backs, cleaned and adjusted the rangefinders, and had to work a little more than that to fix a shutter issue on one of the bodies. My 58/60mm lens doesn't engage the flash (who cares), but other than that is fine so I'm just going to leave it.
For unscrewing stuck screws - spray about an inch of WD40 in a plastic cup and let it settle for a day or two. You'll get nasty cloudy substance on the bottom and clear liquid on top. I found the clear liquid to be a very good all purpose thin lube (without the long term sticky property of direct WD40 application) with good penetration qualities. Apply a little of it around the screws and let it work it's way for a few hours.