Nick;

...permanent?...nothing is permanent, the temp gauge assy CAN be removed from the car, but that would subject it to unnecessary mechanical insults... the connection to the temp sensor is NOT a wire but a (potentially fragile)capillary tube, which CANNOT be disconnected from the gauge...that is why I suggest bringing the boiling water to the car for checking it...not the other way around!

I have now posted a pic showing the cal marks on the SwEm Service Notes page... if you check it, and the calibration is way off, (extremely carefully) hold the pointer shaft and equally carefully adjust the needle position if necessary, but again, I recommend against trying to make any other adjustments on the calibration unless you are comfortable working with Bourdon tube pressure gauge micro-mechanics or maybe are a watchmaker.

I'm still interested to know the cause of the oil leak at the fuel pump.

Cheers