You might try running a lighter oil. Once machines wear like this, there tends to develop a lot of viscous drag or oil shear when using standard 68 weight way oil with all its tactifiers. I have run similar machines with high ratio cable drives and plain bearing ways and had good results with 32W hydraulic oil. If you place your most sensitive indicator against the chuck and traverse the table quickly for a few passes, you may see that the thicker 68W oil develops an undesirable amount of lift with the worn ways. These machines were designed to float on a very thin film, a couple tenths at most. I agree that your ways are worn but this might get you by.