My cure... it worked for me after many 'fob hassles':
- Go to that well known auction site and order a spray can of electrical contact cleaner
- Take the fob apart, remove the circuit board and blow out any accumulated 'trouser pocket fluff'
- Spray the pcb liberally with the said electrical contact cleaner
- Decant some cleaner into a small glass dish (or similar) and soak the circuit board for a couple of hours
- Remove the board and 'blast' it with the spray - particularly where the buttons are
- Allow the board to air dry
- Reassemble the fob
- Bob's you uncle?
Worth noting... The contact spray fumes may be hazardous; so do the job in the garage/garden shed or out of doors!