It will oxidise immediately on exposure to the 'air', so leave it alone and it should be fine if a little 'unsightly' depending on how big the dunt is/are.
If black, a permanent marker will hide a host of woes
H
Agreed, salty water is the only enemy, although 20 years might have an effect
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Watch the black marker though, some contain acids that can affect the alloy, i'd use enamel paint if you wanted to protect it
Sandy