Tightening may help, but that adjustment on top is because the gears are tapered. Adjustment works great for setting new gears with a straight taper. Once the gears wear and have a curve in them they can't really be adjusted back to a new feeling. They tend to go from really loose to over tight. Nothing to lose trying adjustment a worn gearbox. Move the allen screw a flat at a time and test drive. Keep track or mark the screw so you can return to the original spot. To tight and the vehicle will not track straight will tend to settle left or right of center. When the steering box is centered it is designed to have a tighter fit in the gears to prevent wander.