Only part that contain iron is the radar aborbent coating.
US MIC bloated about the "baked in" radar aborbed material, that doesn't need repaiting.
Means rust could mean permanent damage to the radar absorbent material. At least if we go by the USA military interviews.
Of course there is a chance for that they lie. Or I misinterpret it.
From wiki :
The F-35 has a fibermat radar-absorbent material (RAM) baked into the skin, which is more durable, easier to work with, and faster to cure than older RAM