Question and answer culled from Internet mailing list or Usenet newsgroup. Note that these comments will apply to other Macs with similar keyboard.
Some of my SE's keys don't work
Two of the keys on my SE's keyboard do nothing when pressed - the left shift key and the number '9' on the numerical keypad. Can they be fixed? The keyboard has the model number 'MO116'.
ANSWER: You're in luck. Keyboard MO116 is just about the best Apple ever sold, having a svelte footprint with no dumb IBM keys, and the key switches are rugged, individually replaceable 'Alps' keyswitches (unlike the keyboards that followed where you had to replace them all at once, at a price more than a new keyboard). It's well worth the effort to keep it running, as you'll never find anything else as good.
The key switches are the same as used on the Extended Keyboard 1 and 2 - Apple part 076-0209, and should be available from any Apple dealer. Though as I recall Apple sells them in tens, so you may want to check around to find a dealer who has some in stock and will sell you one.
If you are really adventurous, and have any good electronic surplus stores nearby, you might want to look for a junk keyboard with the same style key switches - they are pretty common.
The replacement procedure is basically flux and desolder, being real careful because the traces are pretty delicate, then solder in the new. Check Larry Pina's Mac Classic and SE repair book for full details.
You might also try putting a drop of WD40 down the shaft, and then pushing down firmly and rotating the key slightly to burnish the contacts - this works wonders on Mac 128/Plus style keyboards (once had one on which not a single key worked, yet brought them all back to life this way), but never had to try it on a MO116.
The keycaps are easy to pry off without breaking as long as you take them off evenly and don't allow them to come off at an angle.