Thank you for starting the thread. Looks like we are in a quite similar situation. I have finally put together my gearbox on Saturday and it shifts nice on the bench. Only the fifth was really hard to engage and disengage. Has improved after several tries but still harder than all the other gears. Also reverse shifts nicely. On the other hand I have dissambled the fifth and changing the gear as well as synchro rings.Hi,
so, I checked the shimming and it turns out it was not centred properly - also not far off, so 3/4 could be shifted straight still.
After playing with my available shims, I think I got it right and now it shifts nicely through all gears and out of 5th as well - with and without retainer plate. It’s actually pretty simple to adjust once it is understood how it works