Whether you need to unsolder all the keyswitches depends on the keyboard -- there were 4 types, but only one -- fortunately the least common type -- needs much work. The best, and original, was the type using Futaba keyswitches, which have a white body. These are easy to remove, one at a time (desolder the connections, then release the clips which hold the keyswitch in the frame). I've seen a couple of pictures on the web showing the different types but I can't seem to find one right now :-( The normal way to fix faulty ones was to replace them. You can still sometimes find switches available from people who've dismantled machines. If not, I'd try removing the faulty keyswitches and cleaning them by swishing them in a small bowl of iso-propyl alcohol, or squirting IPA followed by switch cleaner through them. Finish with a good-quality low-residue switch cleaner. These are generally based on IPA with small amounts of very light oil (not usually silicone, as it creeps too much and gets into everything). Do not use anything like WD40!

Pete Peter Turnbull Network Manager University of York