Couldn't stand it any longer so I've been fiddling . . . and it seems to have cured the "not getting into 5th gear" problem.
The before photo shows the linkage after the top hat bushes have been replaced.
The after photo shows the different positions of the parts, in this case, for stopping the gear stick overshooting the 5th gear position.
I did this on a 2007 JTDm.
Record the starting positions of the parts and also the torque to undo the Nyloc nut!!
With someone inside the car preventing the gear stick from moving from side to side:-
Slacken the Nyloc nut, green arrow, with an M13 ring spanner, just enough so the parts indicated by the red and yellow arrows can slide over each other. Move the part indicated by the red arrow away from you, as viewed in the photo, relative to the part indicated by the yellow arrow. Tighten the Nyloc nut again to the same torque as you found it.
Check you can get all the gears - then road test the car.
You don't need to remove the battery/battery tray etc and it takes 5 minutes. Because it was trial and error, I don't know if this is the official way of adjusting the gear selection, but it worked for me.