** be aware, this is for a UK based car, so steering at right side.** This for the passenger side!!
Just a few notes Theo to help other 928 owners who might want to do this work.
1) The passenger and driver's side window guides are handed, so you must get the correct part numbers as shown when you order them. The driver's side cost £26 for the pair and the passenger side was £36 for the pair. Exactly why they're more expensive I cannot say as they look identical just orientated differently. See detail instructions of this process on the driver's side work I started with. You can see the 'tie-wrap' temporary bodge that many people do as a fix. Problem is it puts the guide out of line on the slide bar and makes your window motor work harder as there is more drag. Best way is renewing the guides.
2) When removing the bolts for the window guides, start with the bolts holding the lower guide first. Star by using a long 10mm spanner for leverage to loosen them as they will no doubt be quite tight after 30 years sat there. Then unwind them using a 10mm socket to speed things up. Undo the top guide last. You will no doubt need to move the window up and down slightly to access the bolts as access is limited. Only move the window is very small steps. I have shown pic's of the various positions that access the bolts best.
3) When the window slide bar is loose, carefully pull it towards the back of the door to the left. When it slips off the holding bracket down inside the door, it will then be possible to lift it clear of the door for renewing the guides. Grease the bottom of the window slide bar before reinserting so it will easily slip back onto the holding bracket down in the door. Use STP oil treatment on the slide bar to get the tightly fitting new guides on. You can see how the old ones have worn away on the old 4 prongs that slide up and down the window bar; hence the rattling when lowering/raising the window after 20-30 years.
4) To make sure it is seated correctly when reinstalling, align the window slide bar top holding screws through the cut-outs in the door panel; see pic's.
5) Make sure you take notice of the correct orientation of the old guides on the window slide bar so you can correctly install the new guides. This is important when fastening them to the window upon reinstall. As is assembling all the bolts to leave a little play so that when you close the window fully for the first time, it can align itself in the window guide seal. After doing this, now tighten all the bolts super tight.
Hope this helps other 928 owners. Enjoy the sound of 928 windows winding down with no rattles!
best, Dave.