Interesting for historical (engineering) reasons.
As the oven control runs directly from 110VAC, I assume, that this glass part on top of the heater winding is sort of mechanically acting thermo-switch only, not an NTC. The probability of that is high after all these years. Please check this part by a continuity measurement, and also the winding resistance, if it's burnt.
Maybe there's simply an open soldering junction.
In the end, the whole assembly is an OCXO, not a TCXO.
Frank