Hi
Looking at mine a bit, it almost sounds as if you may need to replace the entire rear housing. I didn’t think about the rust inside, these are sealed units and rust building up in inside is not a good thing.
I have never had to replace anything on mine, as pressure rated pumps go it is nice.
If it is less than five years old, I think it should be under warranty. If that is the case, maybe forcing things isn’t such a good idea.
I just talked to my pump guy, he speaks only gibberish and Google doesn’t make a translator for that, but I think he said if you can get a couple of good photos he ought to be able to tell. He seemed to agree that forcing things at this point is probably not a good idea.
If you do not wish to post the pictures you are welcome to pm or email them.
Biollante