The buckles on the bags mentioned, classical style messenger bags Baileys RELoads etc are Stainless Steel or Nickel-Plated Stainless Steel. They'll start to rust & show corrosion w/in a year if used in the manner intended by the makers. You can slow it down or not, up to you. Usually it appears on the inner parts of the cinch buckle first and only shows up on the outer if scratched or dinged. Do nothing and maybe it won't look so hot & shiny. Used as they're intended the bag isn't going to stay new looking anyway. I have to remind my boss/designer of that all the time. She'll see a 2 year old bag on the back of a messer and it'll be dirty and scraped up and it shocks her because they all look so beautiful and shiny when she makes them that she thinks something must be wrong with that dirty beat to hell bag. But it's working fine, just not new & shiny anymore. They look good used too.

Back on topic, it won't hurt these cinch buckles, that rust & corrosion you see. They still have a decade at the minimum left in them unless you pee on it and leave it that way each day for the first 5 years of that decade. For instance I'm holding a 95' Zo bag given to me today for a new upper strap. The buckle shows wear and corrosion but it works fine and I wasn't asked to replace it so I'm not gonna. It's not as pretty as it was 10 or even 5 years ago but it -won't- fail. They are teh tough, unless it get caught in a vice and mangled or something you should never need to replace it.