The gasket is like an O ring on the edge of the thermostat.
94 FSM lists it as 21 ft/lbs. I found out the hard way that is wrong. I was lucky, the bolt broke without damaging the housing. It should be 8 ft/lbs. If not using a torque wrench, that is barely more than snug. Do not overtighten - that is soft aluminum.To make matters even more confusing is that the FSM actually shows a gasket for the housing in the diagram. But rest assured, there is not one used/needed.
Also if you do remove the housing, be sure not to overtighten the bolts when reinstalling. The FSM also incorrectly listed the torque. I believe it should only be about 11 or 12 ft/lb.
I would break the head off the bolt, heat the waterpump around the bolt with a propane torch and try using vice grips to work it out.I would like to replace my thermostat, but one bolt is frozen. Should I break it off, or grind it off, and then use a bolt extractor? I promise to use anti-seize on the new bolts!