JB weld to the rescue, thermostat housing repair
 

Have you ever noticed how the rubber radiator hose tends to attack the aluminum housing at both places on the block causing pitting and rot? I solved this problem during my last rebuilt by wire brushing the loose metal rot away and then heating a little with a propane torch it to further flake off anything that wasn't solid. Next I mixed up some fresh JB weld from new tubes and smeared on a thin layer. After it hardened overnight it was just like a new surface, smooth and solid. Now the chemicals in the rubber hose can't attack the aluminum because the JB weld protects it.