The "white scrubbie" really does work better than the common green ones. I found it in the sandpaper aisle at Lowes.
This might be the same product.
The
3M site calls the white pads "light duty" for removing fine scratches in acrylic. Maybe why they worked better on the cab scratches than the green ones.
Hope you are able to remove those black streaks before you coat with RMP. It will look sooo much better if it is a completely cleaned and de-chalked surface before you use the finish. But it will shine even if you put it over imperfections in the surface.