Thanks for the advice!I like to drain the coolant below the level of the thermostat just really so it doesn't maybe run into the bell housing when you remove the housing. It's so easy to just suck the coolant out of the side mounted expansion vessel on the 169 model.
original birth one in mine - from S4p - now around 5 years old and operating satisfactorily.
Called up SRS (now NAPA AutoParts) to see if they had something. Thermostat without sensor is £15 all in, so hopefully that'll be decent enough, or would I be better going the S4P route?