[jdblair]

The best mechanic I ever had kept my ‘98 Subaru going past 200k miles. Once during a repair I asked him to do an inspection and tell me if there was anything else I should replace. He told me not to do that, and that any mechanic would always find something, but not necessarily the next thing to break.

He said it better using an expression I hadn’t heard before or since, something like “don’t go looking for goats when your herd is already with you.”

[dumb1224]

Exactly. Old parts of the system will be working if you leave them undisturbed. Mechanics have very good intuitions of this sort of thing.

I read about before there's proper engineering / physics theory about this too, it's like a car as a machine is a linear/smooth physics system with multiple weaknesses. Overtime longtime period of running many places might weaken but it still evolves into a slightly different smooth system, until you introduce a replacement which cause a mis-match of impedance or something like that.

[tass]

Maintenance-induced failures are what it’s called with small aircraft.

You’ll do something to prevent a failure (like, replace an old but functional alternator) but cause an oil leak or engine vibrations because you had to remove the propeller to complete the job.