Hmmm - really strange, I was told originally when purchasing the boat that they were "airline switches" never a failure, obviously not the case right. I am in Southern Ohio, so not the west heat/cold extremes, but certainly hot humid summers and cold winters, but granted, not using the boat 7 to 8 months of the winter cold months.
I will mention, I don't flip the switches from the ends, always kind of place my thumb and fore finger around the base to flip the switch, if that makes sense??? I'm with Sodar, could be the billet expansion contraction and environment causing the problem, only stands to reason with some having an issue and others not? (Plastic and aluminum certainly expand and contract at different temps.)