If the gib is noticeably bent, it could take a lot of scraping to get it flat; and once flat it might be too thin -- with a taper of a few degrees, even a small thickness change will require the gib to move a ways in order to snug it up against the slide . If the gib isn't made of something brittle (like cast iron) you may be able to improve the situation by careful bending.in the opposite direction.
Hopefully the gib and slide haven't worn too unevenly. Are replacement gibs available for your lathe?
