Since I bought my silver MGf a couple of years ago with the intention of restoring it, it has been plagued with an intermittent water leak, the car hasn't been on the road but whilst starting it now and again I have noticed the coolant level would drop or sometimes just disappear altogether, it looked like it was coming from the bottom of the cam belt cover and I originally suspected the water pump however after changing the pump I still had the leak which never dripped out while you were watching it.
Today I decided to take out the thermostat housing because I could see pink fluid on the engine case under the housing and had previously replaced the thermostat and wondered if I'd not bolted the two halves of the housing together correctly.
When I unbolted the retaining bolt for the housing after removing the coolant pipes, the housing came away from the back of the water pump without any effort but left part of the housing still inside the hole, I removed it with a screwdriver and found that the flange of the thermostat housing had perished causing it to break which is the cause of my intermittent leak.
Because the housing is bolted to the side of the engine block and couldn't move and the rubber seal was still in place it didn't leak all the time only it seems after I had let the engine get very hot and then cool down, some pictures below of the offending part.
So the new thermostat housing is in place, I just need to pipe everything up tomorrow put my new engine temperature sensor in and see if that cures the radiator fan fault, onward and upward as they say.