Reply To: thermostat housing (?)
Hmm, have a spare bottle ready and remove the housing itself , so you can inspect it closely ?
Normally there is a sealing washer. If the hole size is 9mm , then go to any car shop locally (very common in cars) and ask for a 9mm hole DOWTY SEAL
Its a special metal washer that has a rubber-plastic insert in the middle.
Failing that, ask for “MANNOL THREAD SEAL” and wrap the bolt with that seal tape , a thin layer 2x then screw in.
One of these suggestions should work but if its the first time the bolt came out, the threads should not be damaged from removing it.