rear sight out of plumb

[chaneylake]

I picked up my Shiloh Sharps .40-65 from the gunsmith on Wednesday, I had a recoil reducer installed, during the process he removed the stock and rear sight to install the reducer. I shot the rifle yesterday in basically a straight-in head wind, "no cross wind at all", I had to adjust the windage 2 1/2 clicks[little lines/marks] to the left to be able to hit center of target at 300 yards.

pryor to trip to gunsmith "zero" was "zero"

what are my options? remove rear site and then reinstall just to see what it will do?

I have never liked the idea of "shims"

your ideas/opinions will be appreciated