Have you tried resetting the mesh of the steering gear and sector gear?
Sounds as if there is too much fore and aft end play in the sector gear's
shaft - which of course would, after much use, 'round off' the teeth of
the small gear. To reset this, take the gears out of mesh by loosening
the collar under the steering wheel bushing, pull the wheel up. Then
deal with the sector's fore and aft play by inserting approprate shim
washers, moving the sector closer to the steering gear. Finish by pushing
the steering wheel down the collar up and tightening it. When done you
should have perhaps 3" of steering wheel movement before anything down by
the wheels moves. (this would mostly be play in the rods themselves not
the gear).