I am not really sure but my first thoughts are trying a Mr clean magic eraser. if doesn’t work, diluted bleach water. Still doesn’t work, power washer and last option primer and paint.
I really like then elbow grease range, spray some on and leave it for 5 mins then used a microfibre to clean it. And if there are still some scruffs after then I’d paint it x
I would use bleach and soap and a tough scrubber. Then repaint it with spray paint.
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I think I’d repaint it too, but if possible maybe take the existing paint off first so you don’t end up with that layers and layers of paint thing going on.
100% I would just repaint it. Some of those are scratches and won’t come off