At post #629,
I have been looking more closely at the image of the part on the trolley. (post 588) I have inverted it and shifted the colour markers with this result. Centre right of image there is a rounded star shape, right next to the line marked on the disc.
A witness mark from something adjacent ? to me it looks like the shape found in an oil pump, and beyond the mark itself a discoloured area.
............
From an engineering perspective this is way beyond my field of expertise, but as seen previously there is a wealth of eng. experience on this forum ... any ideas ? or just a co-incidence ?
TR