I'm trying to change the fore-end on my 3000 pump. In order to take the fore-end tube out of the fore-end, I first have to unscrew the fore-end nut. My problem is the nut will not turn. I've dropped kroil in the threads with no help. I put it in the freezer for a couple of hours, no help. I'd apply heat but that would burn the wood fore-end. Where these loctited when originally assembled? Any help would be appreciated. Thanks, Dennis