There is also one small video where I am removing the clutch pack. If you look carefully you can just see the spring decompressing as I undo the allen bolt, is that normal?
The spring applies tension on the pressure plate to engage the clutch. What you note is tension being released. In real life, the clutch rod would push against the spring to relieve tension on the plate.
I really don't understand your method of investigation, Filmcamera. I would have reversed installation step by step. Is this the order in which you approached inspection. The clutch carrier (housing) would be the last part removed and likely wouldn't be removed at all.
- Unbolt and remove the clutch cover.
- Remove the clutch disc.
- Remove the pressure plate.
- Remove the diaphragm spring and ring.
- Leave the clutch carrier bolted in place.
- Compare the dimensions of the replacement parts to the dimensions of the parts they replaced.
If the all the replacement carrier's dimensions are the same as the original, what you'll use is a tossup. You asserted that the original had "wear" marks. Post a photo showing them. The carrier should have a fiber stop disc installed on its shaft hub.
daveson alluded to that. Did you find one on disassembly?
As far as the clutch nut is concerned, some people have reused them without incident. Whether the engine was never run after the installation could be irrelevant.