The hood is a pretty thick hunk of metal...don't worry about possible rust effects (if any), as it will be surface rust at best.

A body shop should be able to repair the damage fairly easily. It won't be perfect however, unless a whole-hood respray is in order..

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car