So here's a photo showing, top to bottom:
1. Waxtstat/thermostat from my 2.0TD oil cooler diverter.
2. Waxstat/thermostat from another Audi oil cooler diverter.
3. Waxstat from an '85 Jetta TD thermostat, just the center portion of the thermostat. 83 degrees C.
4. Waxstat from a '85 Volvo 2.4TD thermostat, just the center portion of the thermostat. 87 degrees C.
There appears to be two different sized removable pins that can just be pulled (thanks Ngoma) from the non-working waxstats and pushed into the working waxstats, the pins having different tops depending on the application.
I called my local Bosch shop and they said the actual waxtstat for the IP advance (Bosch PN 1467202302) is no longer available.
There's an excellent description of how a thermostat works on Wikipedia here, it explains how the wax works inside a thermostat:
https://en.wikipedia.org/wiki/Wax_th...ve_thermostats
I'll need to select a thermostat with the correct temperature rating for each application, a hot one, above 190 degrees, for the oil cooler circuit and a colder one, around 160 degrees, for the IP timing advance.