Performed the thermostat change today - replaced a "MotorRad" brand with Behr. Successfully completed the required breaking of a housing bolt. Able to get housing bolt out by removing housing and grinding down remaining bolt, then gripping with a vise. (Could not get a grip on it while in the car.) Also got by without needing another housing-to-head gasket because the gasket stuck entirely to the head.
Temperature reading has changed from just a hair under 100C to somewhere in the range of 85-90C.
Housing had no corrosion at all, interior of the head that I could see also looked good.
ANTI-SEIZE.
Ken300D