Heating Question

[Sgt_Nutz]

Any heating guys out there? My Superstore hot water expansion tank is leaking from the Control connection. It is a Honeywell Aquastat and it is leaking from inside the immersion well not the plumbing connection. The hole Control box is corroded and needs to be replaced. It looks easy enough to replace for $100 or so myself. The problem I am having is removing the immersion well from the tank. I tried unscrewing it with a pair of channel locks put it will not budge. I didn't try forcing it to much for fear of damaging the tank. What do they usually use to seal the threads in this type of application? Can I safely put more pressure on it and unscrew it from the tank?

Thanks, any advice would be appreciated.