After cleaning up the gib by hand, the slide is far, far better. It still gets very tight near the far end of the travel, but now doesn't sieze entirely. I am also now able to remove much of the slop at the near end of the slide. It still exhibits a 0.003" movement at the edge of the tool post, but that is a small fraction of what it was. I still cannot call it good, but for many purposes it is good enough. Single point threading, for example, only requires typically less than 0.100" of travel on the compound, and I can work near the far end of its travel to provide enough rigidity. It s good enough for a cosmetic taper. Forget about trying to re-create an R8, JT, or MT taper on a tool, though.