I wouldn't trust the dealer with this. I'd attempt (as others here suggested) chemical decontamination/iron remover followed by clay bar on an out-of-sight spot (after watching some pros do it on YouTube). Don't forget to apply some paint protection over the places you used the iron remover.If it were mine, I would not try to correct the brown spots myself. Let the dealer do it.
If you're not comfortable with 'prosumer' detailing, find a higher end detailer with good reviews and references.
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