I have just installed my second gasket on the thermostat housing. This is my only leak after doing a complete head rebuild.

I do not know why it will not seal. I used gasket glue and even put some thread sealant on my bolts for the thermostat housing. the gasket matched up perfectly to the housing.

The thermostat seams to seal fine. its just between the head and the housing.

 

Is it cracked? I would get another one. 850's, 70's, and 960's will work.

 

Did you try installing it dry? I've never used any "gasket glue" and never had a problem.

 

DID ANY LONGER SCREWS from somewhere else get mixed up with the thermostat housing screws? Corrosion is an issue, sometimes Wurst super silicone on a clean surface works as a thought to solve your issue.