I had the same problem with my thermostat housing. I had repaired it with Devcon 10760 Gray Titanium Putty, 1 lb. Can. Be sure to bead blast the housing before using it. It is the most chemical and temperature resistance version they make.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
I just realized the price of that stuff really went up.
I included a before and after pictures of my housing.