bearfoil - but the rest of the world , including those who have seen and handled the part in question seem to take the view that it was mis-machined. These people will include RR engineers, EASA people, Aussie investigators and the AAIB. FAA BEA and Airbus will have also had a piece of the action by now. Do you think some awful conspiracy is in place involving all these organisations?
In this part of the world end mills are rarely used to machine bores. Bores are drilled, reamed or bored, all of which processes provide the minor circumferential scoring seen in the bore. Wear frettage would be much more irregular in appearance.