The stepper motor is standard, and easy to obtain. I've carefully examined the screw thread. I see absolutely no signs of wear - as is reflected by the machine's light use. I can't remove the stepper motor because of the apparent way its been bonded to the screw thread itself. I can't remove the motor and the screw thread in one go because if it's length. The only way I can envisage getting at it is by removing the gantry sliders so I can drop out the whole of the Z drive mechanics out. The gantry slider rails are an interference fit, and I see no simple way of removing them. Your quite right. I would not consider buying another machine like this if you can't swap out stepper motors. That's why I chose to make the forum post.