If there is so much wear that the gib at full adjustment does not reduce the clearance to zero, then either make or have made a new, thicker gib..
Or, as I found on a very worn lathe: take a 12" long feeler gauge and put in beside the gib to take up the wear. It sounds like a 'hack' way to accomplish reducing the clearance. BUT, it must be a well worn machine, so unless you are going to go through the time and expense of regrinding the ways, the dovetail on the saddle and compound etc, then take up the clearance with a hard shim: aka: feeler gauge stock..
You can take normal length feeler gauges and try various thicknesses until you find one that will work then buy a full length piece of feeler gauge stock. Most tool retailers have individual 12" feeler gauge in various thicknesses, and I know feeler gauge stock can be bought by the roll, I have .005" and .010" in a roll. I'm surprised how often I use the material as shim stock.
DualValve