I removed the hopper this year to install the jacket and replaced the gasket in the two areas that the hopper sits on. I hope I got a good seal but cant be sure as I cant see how its fitting once the hopper is back in place. How critical is this seal, should I be concerned?
Don't be concerned at all. The reason for the gasket on the hopper is for vibration. Metal against metal with the fans running will drive you crazy. Also, make sure your rust preventer in non-combustable.