The thermal breaker is simply a bi-metal strip calibrated to
open if to much current is being drawn. The contacts are often
a problem with the original switches.
Sounds like the builder contaminated the contacts with something
or possibly bent the bi-metal spring.
The brass studs inside the switch wear also and can give you
an open.
For fifty bucks your problem is gone and you shouldn't have
light switch problems again for another 55 years.
Just don't try to get by with the cheap switch, it really is
tinny and a piece of crap.
dg

Denny G
Sandwich, IL