When you say keyboard innards you mean you put this part in the dishwasher?Show Image(http://geekhack.org/attachment.php?attachmentid=3328&stc=1&d=1248570331)
Well..... that's not good then. Capillary action alone means some water soaked into the membrane.
At some point here I'm afraid you'll need to open up the keyboard and do a nut/bolt mod if you want to save it. Wipe down the sheets with 99% Isopropyl - I've found that's safe on the Model M membranes.
But before you do that try reseating the key LOTS of times. If that works you may not need to go through the nut/bolt hassle.
Update: I put both keyboard innards in the dishwasher and let them dry out in my hot car for 6 days. Both have the exact same problem they did before, across 4 different computers... The newer one is the really weird one: I press space and it sends a space and a carriage return. I press the down arrow and it sends a down arrow and a numlock. I wish I could restore this one because it has every single rivet intact :(
Hey Ranteki, nice web page and mod!
Another happy USB enabled nut/bolt modded Model M user!
If you have 17 other Ms, you could test swap a controller. Then we'd know for sure if it's a membrane or controller issue. Two Ms with an identical problem that nobody else here had before pose an interesting puzzle that needs a definite solution. ;)