Don't know specifically if they inspected the thermostat... I had mentioned to them that after I replaced the radiator with a larger volume one, the temp gauge in cold weather never gets above 1/8 or so.

Why they say they'd replace the whole housing ("sub-assembly") I don't know. It's my understanding that the TDC sensor is a separate component - is this true? They took two hours of labor to inspect wiring diagrams to narrow this down.