Aluminum trim water stains

[Matlock]

My truck box has white wrap plastic on top of the original Uhaul decals covering the entire box. Basically impossible to remove any of it. Problem is the aluminum trim that covers the bottom skirt around the box has blackish water stains on the white panels below that trim. Like the aluminum has oxidized and the rain water leaves the streaks below it.

Any ideas on what will remove the stains? I've tried basic household cleaners with no results.