This has been asked several times on the board. There is nothing to clean the jack plate other than soap and water. The stain that youre seeing on the jack plate is etching in the anodize finish which is usally is marked by the the water line and below. Likely a lighter color than the top half of the jack plate. If not too bad, the color can be masked (made darker) by spraying an oil such as WD 40 and wiping off. The stain is caused by nutrients in the water which attack the finish. The harder the water the quicker it can turn color. The best prevention is to wipe the jack plate off as soon as the boat is loaded on to the trailer. Sorry this doesnt make you feel any better about the question you asked.
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