Rob,
Re-reading I should have worked out that it wasn't the spindle motor but it was the only thing I could imagine moving on a halfway logically assembled machine :-(
I suppose all the vendors of ball screws should have a recommended shopping list of Ball Screw, Ball Screw Supports, Ball Nut and optionally Motor Mount, Motor Coupling and Motor, with a brief explanation of how and why, the market has clearly moved to a point where there is no research prior to shopping,

- Nick