Thermostat Gasket

For me, not 100% sure. I used Ultra silicone first on both sides of the gasket , cinched it down, let it sit for 24hrs and torqued it to 15 ft lbs. They are 3/8th bolts, should have taken that. Put antifreeze in and started the engine, it leaked by the time the engine got hot. Poor gasket quality, I don't know, over torquing and warping the housing? I did add washers to the bolts with the silicone gasket, torqued to 23 in lbs. No more leak.