Thermostat housing leaking

Thank you all for the suggestions. Have tried doing what you said. I made another
gasket out of thick paper. Put Permatex on the intake and the thermostat housing.
Reassembled this morning and leak was still there.
This problem started last fall, up until then no leak. Pulled thermostat off and put flat edge on it. Looked a little uneven so I got a new one. It is a chrome steel housing. Had same problem with new housing until I made a gasket, put Permatex on the intake and the thermostat housing. Let set over night and assembled the next day. No leak until last month.
Anymore ideas as to what to try next?
Thanks