As you say the machine is 10 years old, does it CURRENTLY have adjustable nuts on the lead screws? I thought they were a more recent development. My own machines run quite happily day in day out at 60IPM on the closed loop controller, but 40IPM is more reliable with open loop steppers. I would suggest that simply buying a new set of lead screws and adjustable nuts from Taig would be a good investment. We change them on 'production' machines once they get to the point where backlash is getting unacceptable in the middle of the screw when you have trouble getting to the ends. Jewelers and the like tend to do a lot of work in the middle 2 or 3 sq inches
One thing that is always worth doing before starting work is simply to jog the machine from corner to corner on the bed a couple of times. Helps 'wake it up' and gets the oil well distributed.