My theory: I am of the opinion, that the failure in the switch is caused by turning the key when the steering wheel is locked and resting against its limit. I think if one first moves the wheel to a mid (slack unbound) position before turning the key, so as to turn it whilst the wheel position is not binding it. Although the "bind" is so slight to be hardly felt, the fixture may be delicate enough to wear out over 5,000 to 10,000 turns. I relieve the stress by moving the wheel off it's locked limit before turning the key. We'll see how that works out......over time.
Just my 2c

Rusty