When you say the switch is failing I take it you don't just mean the metal is tarnishing?
No some of the buttons are not functioning. We have many others in suitable environments, that are still working ok. Its either the swimming pool environment, or we have just been unlucky. This one, the faceplate fell off, the push in contact fixings failed (the welds failed). My money is on the wet, warm chlorine air, doing the damage.