[Walt Fricke]

The kicker here is no 5th, and no reverse. If the fore and aft adjustment were out of whack, you'd expect one to work, and one not to. As well as issues with 1&3, or 2&4. So the finger would point to the side to side (rotational) indexing being off. 5/R work differently than the rest in terms of how movement of the shift lever creates movement inside the transmission.

My guess is you will find either the plastic cup bushing at the bottom of the shift lever is worn out, or you will find one or both of the bushings in the shift coupler are even looser than they are designed to be, and you weren't able to rotate the transmission shift shaft quite enough in the direction it needs to go for 5/R. It works by a finger on the shift shaft rotating into a slot milled into the shaft the 5/R shift fork is attached to. If the finger doesn't move enough to engage the slot, the shaft can't be pushed/pulled back and forth. I think the tolerance for misalignment is smaller here than for 1-4.

But replacing all the external wear items is the way to start. Keep us posted.