I have posted instructions on the SonikMatter forum some time ago (and on Keyboard Corner) in detail on how to clean keyswitches and determine if the strips need replacement. The process requires some knowledge of how to do mechanical things. The keyswitches each have two contacts (they connect at different points, and the difference in time is used to determine how much force was applied), are carbon mounted in a grey rubber-like material. Some of the Nord and Korg models use the same Fatar keyboard assemblies.
Reaching them is not super easy. First, the end blocks must be removed, then the bolts underneath that hold the two parts of the "clamshell" together. Always being mindful to keep track of where cables go through, so they can be placed back in the right place so they will not be crushed and shorted out. After the top and bottom are separated, the "keybed" meaning the entire assembly of all the 88 keys must have al of its screws on the bottom of the keyboard removed, so it can be removed. The Treble and Bass connectors will have to be carefully removed on the computer board end, and the small connector near the mod wheel that carries aftertouch signal very carefully removed (mark which way it goes back).
You will then turn over the keybed, and you can see the key contact boards, two boards (bass and treble). Each board has a lot of short bolts that holds it in place, and they all have to be removed, so it can be turned over. You will then be able to see the grey rubber-like strips. Most are 12 key in length, except at the end. Count up to which key is sounding improperly - do NOT remove any stuff that does not need to be removed, make a pencil mark on the keyswitch to guide in peeling up the rubber very carefully. You then inspect it under a good light. In the event that it is torn or cracked, you will have to obtain another strip. Kurzweil will not sell direct to end-users, so go through someone Like Sweetwater (authorized service center). Note that the strip will fit backward, but ALL 12 notes will then sound at full volume all the time, so be careful. If the strip is not torn nor cracked, clean the little "cup" carefully. I use a Q-Tip wet with pure alcohol. Rubbing alcohol usually contains mineral oil, although pure isopropyl alcohol is OK. There will likely be a very small, just visible speck of crud. Said crud may be on the circuit board also. After cleaning and letting it dry, you will have to carefully put the rubber strip back down. Something like a straightened paper clip is useful to push the little rubber protrusions through the small holes that hold it in place. BE CAREFUL not to damage it.
Reassembly is the reverse of disassembly. If the above sounds quite difficult, pay someone who does that sort of work to do the job. NEVER BLOW COMPRESSED AIR into the keyboard, you may do extensive damage not only to the keyswitches, but also to static sensitive components.
Someone has posted a series of pictures on the web at this link: http://tk386.com/k2000_keys/ It shows some idea before you open things up of what they look like inside.
Our church had that problem a few years back with our Korg N264...or something like that.
My uncle then told us it needed to be cleaned so he sent it to either the shop or a guy that just new what needed to be cleaned.
I had a similar problem, but I opened the unit, carefully cleaned and didnt quite get the key to work perfectly. The rest of the keys notoriously improved their performance though.
If its not a dirt problem, what would be it?