@alistair , Alistair, Use the disassembly guide below to take your watch apart and clean the buttons perhaps if need be then you will have access to change buttons. Use a soft cloth or Qtip dampened with 90% Isopropyl Alcohol to clean around the buttons and contacts. Good luck.

I hope this helped you out, if so let me know by pressing the helpful button.

Garmin Fenix 2 Motherboard Replacement