Our two motors suffered from a long and terminal case of rust-itis. It starts with a dermal complexion rash and if not promptly treated rapidly spreads, causes bloating and in the end given enough time all that will remain is a umber colored stain.
For steel to rust you need two basic things. Water and oxygen. Neither by itself causes rust, you need the collusion of both of these ingredients. Now if you add salt to the mix you can dramatically accelerate the process. But my essay isn't about rust, it's about how the water got there in the first place.
I have two recent examples. One is a winch motor in a forward anchor locker, and the other is a autopilot hydraulic pump located in the lazaret. In both cases the owner's aver the motors were working the last time they used them and I believe them. My inside voice however is mumbling the last time these motors were used Ron Popeil was selling spray on hair in a can.