How to fix a bad key?

I'm wondering if anybody can point me towards a resource for replacing the rubber switches in the keybed? I have a key that only sounds intermittently/when you press extra hard. I ordered replacement switches as I assume that the problem is most likely caused by an aging switch, and want to open up the synth and get in there. Do I have to take the top case off to get to the keybed or can I access it from below? Any advice on this? What would the procedure be for removing the top of the case (I've gotten into the bottom to replace the ribbon controller and battery and stuff, haven't done any work on the top part yet so any advice/links would be greatly appreciated) tia