Doh! There is testing, and then there is stressing. In my excitement of cleaning and testing the thermostat, I think I went too far.
This clever little thermostat was nice to see clean up well in the blasting cabinet. Dull and old became fun shiny brass. Attacking it with a heat gun made it expand like magic. I must have applied more heat than it’s expecting, thereby cracking part of the accordion or damaging one of the solder joints. A unique smell presented itself, and I could hear the liquid inside when I shook the unit. No more magic expansion.
The irony of breaking it, while in the process of making sure it works is not lost on me.
I was able to find an original in very good shape on The Samba Classifieds. Another expense I would have liked to avoid. I will be more gentle in my cleaning and testing this time around.