My heater stopped working completely and I found it was the resistor again. I've cleaned up the disc in the pic above and it sort of works but moving the disc about greatly varies the speed of the fan.   My question is what does this disc do? I assume I can't fill the hole up with solder otherwise there wouldn't be this whole setup in the first place?   Also, does anyone still sell them new apart from Pug? GSF and ECP don't seem to do them.