I agree, I think the housing needs to come off unless you are replacing the water pump. I figured when I rebuilt my engine, I would leave the thermostat right where it was because I don't think it leaked before I disassembled it. I figured wrong, it leaked with no pressure at all. When I removed the thermostat, I just couldn't believe how hard and cruddy that gasket was. Found some serious corrosion in that aluminum tube where that 2" hose goes too. Swapped it with the one from the other car, and checked both thermostats at the same time.