Were there blacksmiths coming along who helped repaired rusty armor? How exactly did they do this?
Which parts of the armor got most rusty and what were the disadvantages.
Were there armors already that were rust-free? (given that the armor was steel or iron)
It actually takes an awful lot of rust to structurally damage metal, so it wasn't a huge problem.
The cure for rust was to put the armor in a bag or barrel with sand and roll it around until all the rust was rubbed off.