There are several possible causes for the play you describe.
Looking at the exploded parts diagram in the handbook the rack is a separate item fixed to the back of the main quill with screws at top and bottom. I suspect that if the fixings worked loose it would allow some slack there.
I can't see if there is any provision for mesh adjustment between the rack and feed spur, though you could try shimming between the mounting face of the rack and the quill body to achieve that.
The other more likely possibility is wear in the quill top radial ball bearing and bottom taper roller bearing. There is a nut and washer on top of the quill spindle above the top bearing which according to the handbook is provided to be adjusted to take up axial play. It goes on to say that 'This nut can be reached when the quill is removed from the machine.' Looks like the first thing to check.