I have a 1902 rear sight that has an extremely tight windage screw. The only way you can turn it is to put the knob in a vise (protected by leather) and use the leaf as a lever. The knob does have some scratches that looks like someone tried to use pliers at one time and they slipped. I have soaked in liquid wrench; no change. I soaked in kroil for several days; no change. There is no visible corrosion when you look at the screw threads. Has anyone run into this before? Any recommendations?

Thanks for the tip Mark21. I will keep messing with it.