I have been thinking about your problem. How thin is your gasket compared to the first one you had? It is possible your thermostat is thicker than the alowed counter bore and gasket. Might seal at first, but after it expands and contracts it is not enough. Double gaskets or a thicker one may fix the problem. Food for thought!Boltholes are blind, as far as I can tell the backsides are crack free.
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