Hi Patrick, if you feel confident enough, this is what i did to free up the buttons. Removed the outer case, you’ll need star screwdrivers, then undid the circuit board screws ( Philips-head) and removed the unit completely for access, I didn’t bother to disconnect the battery. Once out I have a Jewellers eye glass as the parts are exceedingly small. Depressed the sticking button and removed the small securing clip holding the button in place. Make sure you’re doing all this on a white linen cloth as the parts are very easy to lose. Once the clips removed the button comes out. There you’ll find a metal washer, a rubber gromit and a small spring. I just gave everything a clean and the spring a slight stretch before putting everything back in reverse.
the tools I used were:
Star screwdriver
Philips-head screwdriver
thin nosed tweezers
A cup to hold the screws
Jewellers eye piece
let me know if this helps.
Michael