Easy" says old mate; "you pay me $1.00 for hitting the pipe and $99 for knowing where to hit it"..
Hmmm interesting that story, I once read a similar story about a retired engineer from .....Annset, I think it was, where he was recalled from retirement to fix a problem on a 727, I wondered at the time if it was urban myth. It was a good story but looks like it was just a story.