65 Dart Wiper Switch Breaker

I suspected the original bi-metal had cracked in half.
I had to cure that fault waaaaay back in about 1980, before internet. I cut an opening in the switch body for wire to exit and placed a more modern cycling circuit breaker on the outside. For those who go through this...
My guess is eventually you will find wear/resistance in the drivers side pivot assembly is the root of the problem. Meanwhile, cleaning out the gearbox and filling with lithium grease will help.