The frame of your 642 is not stainless steel, it's aluminum. The flaking you're seeing is the clear coat. Aluminum requires a different type of finish than steel and it typically isn't as durable. The Colt Cobra that I used to have was very lightly used, but it had very obvious holster wear in certain places (the edges of the topstrap and bottom of the trigger guard). What type of holster are you using? A poorly fitting holster will cause more rapid finish wear than a better fitting one.
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