Any gun cleaning solvent should remove residue but don't let it sit on the metal for prolonged exposure as this can be bad for the finish. I wipe my guns down and then wipe them off and dry them immediately.

If the adjustment screw seems stripped it likely is stripped. I don't know if it can be repaired. A new sight assembly can be had for around $50.

The bad news is that the barrel cutting is modification generally detested by most S&W fanciers. It's a killer on the value. A nice set of correct stocks will run $100 and when you add the cost of a new rear sight you realize that maybe the dealer wasn't being all that magnanimous.

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