I've used grease on the gasket -- or sometimes silicone (the orange/red stuff) -- but only a tiny amount (grease or silicone) -- a little dab on the index finger--spread to thumb and then rubbed into the paper gasket -- my thinking to act as a lubricant as you lever the pump up. I hang the two upper bolts through the pump to hold the gasket. If you have any doubts about the thermostat housing -- I have spares (early B18 and B20) -- $5 plus postage. I doubt sealant will stop a leak if the thermostast "O" ring doesn't seal. -- Dave