Opened up both my front and rear doors.
The third unknown bush is really a slider matt that is glued to the glass. It is not a polymer roller. All mine were intact, front and rear. Couldn't get pic of front one, but the rear one look like this:-
Front do was missing the roller bushes, found this:-
Stuck my finger into the channel, and found this at the bottom:-
Rear one was all good:-
I dont think the slider is in the equation. It would be eaily fixed with some trimmed plastic resin and waterproof super glue.
Did note on every second wind up the the window rocks/rotates a few degrees using the centre bottom area where atttached to the lift mech as a axis point. ie causes the fitting at the top of the glass issue.
In the pic of the missing large bush, that actual centre shaft was touching the channel when this happened. And also you could wobble the glass left to right.
The rears of mine, that have all the bushes intact, do not wobble and do not rotate.
Time to get some bushes made up!!!