Leadie, thank you for your comments, Ive been out of it for a while. Yes there were a number of old LAMES in grey cardigans who condition monitored fuel flow/vibration and performance parameters in my day but they did it on graph paper and almost always generally got it right - changing out an engine or module at just the right time.
As for "on condition" that was where there was a simple Yes/no question regarding replacement and by definition, no safety of flight critical performance item except perhaps windshield wipers and tyres was on that list.
Hard time, not sure what the rules are these days cycles, hours, landings, etc. I would have thought that by now we were doing real time time/temperature/rpm histories for disks.