That is called a recirculating ball nut, and they are widely used in CNC machine tools. Usually the balls get beat up first, then the nut, and finally the shaft. They also get noisy well before they die. Re-balling them is a common thing to do on the commercial units. Some are designed not to be re-balled. However at this point taking it apart isn't going to make it any worse. It is very easy to get new balls. On some designs they actually adjust the clearance by loading larger balls. If it were mine I'd certainly take a whack at it.
Gary H. Lucas