You said older but, that isn't enough. We need to know if this is a brush or brushless machine to start (what year on the ID plate?).

Second bit of troubleshooting: most axis amplifiers and cables on these are the same. You can try swapping X and Y amps and see if the problem is with the axis or the amplifier. If it's still the X axis, you could do the same with the motors or cables, except...

Does the X axis ballscrew turn freely or could the bearings be seized? Common failure for older oil-pump fed equipment is the whole Vactra 2 way oil problem. The restrictor orifices plug, oil stops going to the bearing packs, they're under way covers so we don't notice until something stops working.