Motor failed with window in fully up position. This was fun - not.
this is the complete window lifting mechanism - it comprises two vertical rails, with white clips which slide up and down, connected together by a continuous wire. The window glass has two holes at the lower edge and the glass is secured by these two clips.
If buying secondhand, check the rivets have been carefully drilled out and the holes are not oversize. In this picture, the remains of the old rivet haven't been pushed out yet. If the holes are oversize, the replacement rivets may not pull up tight without the addition of a washer - alternatively use nuts and bolts - but watch out for clearances and alignment if the holes are oversize.
Remove door cover - this is held on by 9 clips; have some available because they invariably break!
see removing door cover
Rip out the white condensation cover. New ones are available but seem to cost around £80
At this stage you should have the replacement winder assembly ready for fitting so you can see how the glass is secured to the guides.
Because mine had failed in the fully up position, I had no alternative other than to drill out the pop rivets holding the two sides of the guides/motor assembly. Use a 3/16" drill as you don't want to open up the holes for when you replace the rivets.
As the glass and winder assembly dropped to the bottom of the door, it was possible with difficulty to separate the glass from the clips. It might be easier to separate if the window is part way down and still secured by the rivets - for me, everything was jiggling about when I tried to apply pressure to the clips!
The glass is firmly held by two white plastic clips, one on each upright.
You may find access easier if you remove both rubbers off the top of the door and poke a screwdriver from the top downward to open up the clips.
Separate the glass and wedge it in the "up" position.
Remove the white plastic spacer (for want of a better word) by drilling out the rivets (also 3/16" drill).
Unplug and pull out the old winder assembly.
Plug in the replacement winder assembly and make sure it works before rivetting it back in place.
Drop the window glass down until it clicks into position on the clips - very satisfying!