I had to fix one once that had a broken/damaged OG glass. I machined a UKicon OG housing to fit and the optics were up the creek and the image couldn't be focussed/adjusted no matter what I tried. Eventually it all came good but only after having replaced the original optical system with No32 lenses throughout.

Maybe Warren can pass some comments as I understand that he has compared the lead screw and other threads but I seem to remember that after a few hours I was pulling my hair out
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