Thanks Stina.
Willy, I was going say that if brake master, slave cylinders or calipers are removed and sat on the shelf with remnants of fluid in them, I reckon they will start to rust and seize very quickly. Experience with brake calipers is similar - if the piston seals leak at all or the boot that covers the piston gets torn and you don't get onto it quickly, even a tiny amount of air interacting with brake fluid soon starts to eat metal.