Harry,
Have you tried adjusting the cross slide to "eliminate" end play as detailed in the Myford S7 handbook? (page 29 in my copy).
It is virtually impossible to eliminate play in a cross slide throughout its travel as there will always be more wear in the normal operating region. A little play does not really matter on a lathe as the tool only works one way if you know what I mean. Play in a milling machine slide is wholly undesirable.
Eric