Those don't look like stains to me. But I can't zoom in on your picture so not sure what I'm seeing. Look more like paint top coat has worn through. Under top coat is a black primer. That primer may actually be a powered coat (IDK) as it seem very hard. Cleaning products like purple power & castrol super clean are too strong for paint and may cause just what the picture looks like has happened. Buffing with a power wheel foam pad that's gritty or to fast (hot) may also cause this condition, so I learned the hard way

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Iron-X is a good product for removing contaminants like iron off paint. These come often from rail lines, when rig is first transport across the country. They also come from brake dust. But I don't see that being your issue.