Thanks ferrydude.
Engine is rebuilt to manufacturers specs.
Age I do not know, but new to us as exchanged for time-ex unit. Less than half TBO.
Could be age or environment, but spanners are saying by the look of it there should have been some indication of it at overhaul. (fairly well established considering type of metal etc)
Wondering what the rest of it looks like, the part we cannot see, based on the part we can.
Second opinion/previous experiences welcome.
Cheers