With only 1/2" of play the box is likely adjusted too tightly. 1 1/2" can be considered normal. Get jack stands under the lower suspension arms and turn the steering wheel across the centre point. There should be no stiff spot at all. Adjust accordingly. There are no new worm and cog parts available so if worn you will have to do the best you can and live with the extra slop or search out a box with less wear. They are hard to find. Don't live with a leaking lower seal. If very minor leakage keep topped up. There may be bush kits for the PV box. They can be found for the Amazon box. Careful reaming required when fitting.