It's astonishing how metal stays together . . . until suddenly it doesn't.
I doubt it was possible to get a clue as to the state of that shaft but there's just a chance the clues were there.
It's very different, but I was due to flight test a Heron and the aircraft was surrounded in tech-staff. I noticed a fine line on one of the engines and got a couple of blokes to rock the aircraft with the prop. The line glistened more on a push than a pull. The Crankcase was split from top to bottom on one side. Goodness knows how long it had been like that but it's doubtful we'd have survived the entire front of the engine breaking away.