For future info, we had the same issue with seeping coolant around the thermostat housing. I cured it by placing it on a block with sandpaper and sanding it flat. The intake was also seriously pitted, I used the same block and sandpaper to clean it up. It was so pitted that I was not able to take it down as smooth as the housing, but got most of the pitting out. This pic of the intake was "in process".
Cal