manual box rebuild

You can get an "idea" of the need to rebuild by the amount of free play when the wheels are straight ahead. The stud and lock nut is how you adjust this excess play out. loosen the nut and turn the stud CW. But if you have wear step up on the center tooth than yes you need to reface that tooth. Otherwise if you remove the play while the wheels are centered than when you turn the steering wheel left or to the right the pinion teeth and the worm gear teeth will be in a bind.