Hi Nick
I've only had my Beocom 2 for a couple of weeks, and as it works fine I've not taken it apart, though I hear they are not the easiest things to work on...
If you decide to take it apart, then I'd be very interested to know what is inside. I'm guessing it is a membrane keyboard, rather than switches, but if you can get it apart it may be obvious what to fix.
It would be even better if you'd write it up so the rest of us can benefit
Best wishes