I have the window problem, driver side rear.
Pesky mother in law tried to use the window, the cable snapped, ran inside the actuator and jammed it. Took the door card off, baulked at the access for the bolts! Looks well fiddly! Anyway the motor is actually OK as you can hear it trying to turn the actuator before it jams tight and the bottom flexible loop was lying on the bottom of the door so I know it's not electrical.
I got lucky and found a private seller on the 'bay who happened to be breaking a 156, got the full mechanism for £9.99 + delivery! Although I haven't tested it yet, doing this is saturday morning's job I think.
Does anyone have any tips for the removal and refitting top part of the mechanism as it looks incredibly hard to get in behind it? Does the inner skin come off in any way for access? Any help appreciated
It is not as bad as I first thought. Once you have got the card off and carefully peeled back the foam liner, remove the large black plastic cover held in by 4 screws below the handle area (I just let mine drop to the bottom)
There is a long rod going across to the door button rocker. Disconnect at the rocker just below the button, then carefully get your hands behind the 2 white rectangular clips that hold the rod in place and squeeze to release them from behind and allow the rod to drop down out the way.
Remove the 3 10mm nuts that hold the motor assembly in place and then the 2 more that hold the slider for the window.
My window was up at this point.
Reach behind the glass through the access point that you have just opened up and about midway in the glass, about 1 cm from the bottom edge you will feel when it joins to the slider bit. The slider has a small fat plastic pimple / pin on it that goes through the hole in the glass and should have a tag coming out of the bottom of which goes under the glass and back up on the outer door skin side and on the end of it is a plastic circlip. Pull this vertically downwards to release the clip (note they are white or yellow depending on age/model). The tag might break but the clip will be OK, so don't worry, just keep it in case your replacement is missing it.
Next push the motor mounting bolts out of the holes and allow it to drop.
Next push the bottom mounting bolt for the slider, out of its hole.
The top one is a bit more tricky. I found the manipulating the lower part of the slider towards the motor and twisting a little with one hand, allowed to be push the glass by the pimple towards the outer door skin with the other hand get the pimple out of the hole in the glass.
Once do the whole assembly can be removed through the access hole you opened up earlier. Its a bit of a squeeze.
Refitting is the reverse. I wired mine up first and tested before refitting, but be careful not to allow the sider to run the end of the mechanism (I did and its fiddly getting it back past the pulley). Also be aware some windows may be auto sensing for trapped hands etc... Mine was not, but if have not checked you may have a different actuator... not sure if this is a problem or not.
Note when testing it, both the drivers and passenger door switches must be connected. Also if you blow a fuse (unlikely) you can confirm if its ok or not by the fact if its gone the switches will not illuminate (saves digging around in fuse boxes).
Let me know how get on, PM me if you want some phone support.
PS. when out, my glass stayed in place, but I did pull it up and down by hand just to make sure it was free. I made a stay out of a piece a wood and use it to jam the glass at mid point down to a triangular bracket that goes from the inner to outer skins at the lower part of the door. This allowed me to drive around while I was waiting for the part to arrive. I know you have your spare already, but just in case.
Also the 3 rubber mounting points for the motor should come with the replacement. Mine was missing 2 so I transferred them from the old to the new one, but getting them off requires you to use 2 nuts locked together, allowing you the them unscrew them off the motor.