Before you assume that the problem is in the steering box, check the following:
that the top and bottom bearings in the steering column have no play;
there is no play in the column-to-steering box link universal joints;
the UJ clamping bolts are fastened correctly and the slpines are ok;
the nut attaching the steering wheel to the column is tight;
there is no play due to wear in the steering wheel hub splines.
All of these will in introduce play into the system.
By the way, the play will increase considerably the closer to full lock the steering is. It is an inherrent design weakness in the Cam Gears worm and peg box.
