HI, If the worm thread is worn on the flanks it will need replacing. Assuming that is not the case, it could be that the tapered mating peg on the lever arm has worn a flat where it touches the flank of the worm. this could ultimately result in the peg contacting the root of the worm before it touches the flank when you try to adjust the play.
I believe the peg may be available for replacement if that is reqd.
Dave.
