Just thought I'd update this having received my parts from Italy (ebay) and fitted them today.
I got 2x p/n 60578402. ( I will keep one as a spare)
just to orientate yourself, if you imagine the whole assembly as 3 distinct parts:
1. The anchor clamp and pin that attach to the door frame
2. The strap that goes between the anchor clamp and disappears into the hole in the door edge
3. The body of the 'sprung' assembly that gives the door it's damping and is located inside the door. (incidentally it is the frame of this assembly that breaks and causes the whole problem)
Well the part I from Italy got had items 2 & 3 assembled together, but it did not have item 1 included.
On my car- item 1&2 cannot be separated, as the pin is riveted through the strap and clamp.
therefore I had to take the newly delivered part, separate items 2 & 3 (strap and sprung body) apart and replace it with my original items 1&2 (anchor clamp and strap)
then fit the whole assembly to the car.
I've read on some models the pin is not riveted (I guess a circlip or something) which would make things much easier, but above detail is what I found on my 99 P2.
It could have been done through the speaker hole I guess, but would be very fiddly. I had the screeching window mech so elected to remove the door card anyway and lubricate the saw tooth cam that operates the window mech and generates all the terrible noise