So, I finally got around to fixing my Macbook Pro's spacebar squeak. The repair is simple and straightforward, as long as you follow these directions. This is for the original MacBook Pro only.

1. Remove the key

   Use a flat and smooth edged piece of metal or plastic to pry up the spacebar. I used the lever of a nailclipper. Slide the metal under the top (screen side) of the key near the edge. There are three scissor assemblies. Use gently increasing pressure along the top edge until the key snaps up. Then move to the next scissor. Don't pull it up before you have all three done:

   

   Then do the same for the bottom of the key (trackpad side). The key should come up easily at this point.

2. Remove and lubricate the metal bars

   The key has two metal bars, the thin one and the thick one:

   

   When I moved either bar I heard the squeaking sound that I had grown to hate. So this must be the cause, these little bars and their mounts.

   Remove both bars from the key, one at a time. Try to not bend the key or the bars too much; they should come off with just a little bit of effort. Now lubricate the bars. I used Vaseline because, well, I had some. Other lubricants should work just as well. I wouldn't use graphite powder, but WD-40 should be fine. Just rub it all around the bar. Then snap the bars back into place, just like you took them off. The thin bar has two sets of mounts, on mine the bar belonged in the outermost set.

   I then applied some more lubricant to the plastic mounts just for good measure. You can move the bars and sense the smoothness now; no more squeaks!

3. Reattach the key

   This is the part some might have trouble with. It's easy if you know how to do it right.

   

   There is a little metal piece on both side of the key area, just to the outside of the outer two scissors. The key here is to position the bars at the correct angle to slide them into that piece's slots.

   Angle the bars at about 45 degrees hanging under the key. Slide the thick bar into the holes at the bottom of the piece. Then as the key is lowered the thin piece should rotate down as it contacts the laptop and slide under the top of the pieces.

   Then just press down firmly on the spacebar. It may take more pressure than you think. If the key action is a bit slow you probably don't have all of the clips engaged. Just apply even pressure all around the key until all of the scissors are engaged to the spacebar. If it doesn't go in, try removing the key and trying again.

I hope this helps! I know they don't make these anymore, but there are a lot of them out there.