I think this belongs in the cast bullet forum, so I will move it there.
Never had to take mine apart, but I note the newer versions use a PID temperature controller. If you get one with a solid-state relay rated to handle the furnace current, you can actually have the control on the outside using a thermocouple probe that drops into the melt. The old thermostat would then either be turned all the way up all the time to surrender control to the outside controller or, if that doesn't work, you can short the thermostat contacts out to force it constantly on, which lets the PID controller take over for it.
There are lots of PID temperature controllers and solid-state relays on eBay.
