Service manual speaks of a perfect world. In the real world, wear happens and it is impossible to get it 100% right. Worst wear happens in the hole in the exhaust housing that the shift shaft passes through as suggested by dave. Grab hold of the shifter handle and see if you can rock it up and down. If you can, the lever inside the housing is also rocking up and down, reducing the up and down travel of the shift rod. I remember trying to put a bushing in the hole 60 years ago. I wasn’t as successful as I had hoped.
When you do the adjustment, favor full engagement of forward to protect the clutch dog. You may then have to go a tad “past” neutral to get it out of reverse, then go back to neutral position.
