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You don't need to take the stock off to do anything with that sight. If the adjusting screw is frozen I would put some penetrating oil on it and work it loose. Add oil, let it soak, wiggle it back and forth, Repeat.
Do you mean that the base is stuck to the left, or that the vertical rails have a bend in them?
Sounds like the windage screw is stuck. PB Blaster kicks rust's a$$, protect the stock and soak the sight assembly down. Don't force it.
Good luck