You might try using comet. Sounds abrasive,but if used gently, the green
product will kinda stick to the surface without dripping too much.Has
bleach in it.I used a regular car cleaner soap  with bleach and a brush. No
problems with the paint on the van ,even though it ran all over it.Leave
the bleach on for as long as posiable.It takes a day for the bleach to
lighten things up.Looks great afterwards.