You are mightily in luck as I have just ripped my linkage apart on top of the gearbox about an hour ago(again - the cleanup and greasing was a short term fix by the looks of things).
I'll be back onto it on tuesday, I think, and will take a set of pics then.
The gate selector shaft is most definately mega stiff in the top bushings and it is this strain that kills the tunnel selector plastic housing.
On top of the gearbox......
Currently Ive got the top shaft out of the housing (tapping it out with a 'bit' of force) and what I need to do now is ream the two bushes that the shaft rests upon, within the housing.
These bushes look like they are Nylatron or Nylon66(graphite impregnated) and I'm pretty confident that they 'swell' ever so slightly over time. And I dont think greasing them helped to be honest (it may even have added to the swelling). The Nylatron should have been self lubricating.
Ive been measuring
Shaft diameter is 14.645mm. You may be puzzled as to this size but believe it or not old measurement standards die hard and its all to do with imperial fractions.
37/64" is a standard imperial size which equates to 14.684375mm and this, I suggest, should be the bored diameter of the bushes!.
And if you take the differance between the bore hole size and the shaft diameter size you get 0.039375mm.......... which equates to '1 thou' clearance between the two.
With the bushes swelled up that clearance decreases to the point that its an interference/friction fit....... which kills the plastic housing as it cant take that amount of strain acting against it.
So the answer is to ream the two bushes back to a sliding fit on the shaft. The tolerances have to be quite precise as any excess slack will be as bad as too tight - you wont get accurate gear selection with a sloppy shaft (any slight excess clearance which you create 7.3+mm from the centreline of the shaft will be magnified many times by the time the excess movement acts at the extremity of the lever arms).
Unfortunately I havent got a 37/64" reamer or an expanding one to fit so I've had to order one today
so that I can reassemble everything.
Its going to be tight getting the reamer in on a straight plane to enlarge the bushes insitu but its do-able (just). If I cant get the reamer in then the selector block will have to come off the gearbox in order to do the necessary work.
Until episode 2 next week !................