I reckon a rebuild will make quite a difference. As a reference for you, there’s absolutely no slop in my new shifter - In neutral the spring loading holds it firmly between 3rd and 4th. The spring loading is strong and needs reasonable pressure to pull it left for 1st and 2nd, then really quite a lot of force to go left again for reverse. I remember when I first tried it I thought something was wrong because it wouldn’t go across into reverse, turns out I just wasn’t using enough force - the spring loading is that strong. Forward and backward into the gears is smooth, only slight resistance felt from the detent springs in the gearbox.