I am having the same problem with my sbe 1. I mean I have hunted it real hard, and thought it was getting cleaned good but the action is slow and it is not ejecting spent shells. What is the name of the break free stuff you are using? I called benelli and they said they could have a gun smith look at it and determine if it would be covered under warranty, but thats a 6 week turn around and I have to cover S&H costs.
One more question when you say you are heating the nut, are you heating the piston or the actual nut itself. Because I can't get it to budge either.
You would think you spend that kind of money on a firearm, they could have a benelli gun smith or two on this forum to reply to some questions!