Thermostat Housing

I had the same problem. Real Gasket worked until I installed a Flowkooler water pump, blew the Gasket out, twice. Went with a Flashpower o-ringed housing, have not had an issue since.
No one has ever commented on being able to turn the thermostat shutter, bottom of the stat. This may or may not be one of the reasons all of us at some time or another have had a problem with leaky housings. Not going to purposely blow antifreeze all over the engine bay by closing the shutter to see what happens.
First picture is closed. Second is open.