Replacement is not that difficult. Make sure the bearing are out in correctly including the orientation to each other. Most have a V scribbled across the outside races.
Usually we hand tighten them, pit a dial indicator against the end of the ball screw and stretch the ball screw about .003 inches using the spanner bearing nut. It takes a lot less force than one would think to do so.
George
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)