A few brave pills later I am into the OXCO, check out the size of the crystal, in a glass envelope, not seen that before. The oven itself is looking tricky, I think the inner metal tube has been "cast' in with expanding foam, which has oxidised, possibly with excess heat as the oven heater died/shorted/age.
Edit; re the crystal size, the lines on the cutting matt behind are 5cm apart.