Get the rust sorted with some Hydrate 80 from Bilt Hamber, grind the rust away to see how bad it is, it may be holed!
Grind back to bare metal, treat with several coats of Hydrate 80 this will turn Black/Purple, if the arch is whole and not hole, lol, then you can run about with the Hydrate 80 on until you get it sorted.
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