On 25 August 2013, Art Pearse in Ontario, Canada wrote:
"Looking at my heater switch, there is a spring loaded pin that is supposed to hold it in either extreme position. Trouble is it locks into the position shown and you have to release it using a prod. I'm thinking of easing the detente profile so it will slip out easily. But then I measured the switch and it has a contact resistance of about 2 ohms, so I'm thinking the whole thing is toast"?

I had a couple of flaky new ones back in summer of 1998. The first one had a faulty switch with intermittent contact (usually no contact). The second one had exactly the problem you show in your picture. This is a manufacturing defect (more accurately a fault in design of the replacement part). Solution is to grind or file away the sharp corner so the spring loaded detent can ride up the ramp when the lever is pushed sideways (two places).

These old style switches have gross motion contacts, meaning that the contacts slide across each other when the switch is moved. Fairly often if you just exercise the switch through a hundred mechanical cycles or so the contacts will clean up and give good low resistance connection.