What did they tell you
sand back, prep wash then spray
This is how i would do it. Sand the whole bar with 600g wet just to take off the gloss. Sand out the flakes with 240g dry then 600g wet making sure they are smooth. Spray plastic primer 3 coats over the plastic areas, spray the color over the black areas, get bigger with every coat 4 coats color then 4 to 5 coats of clear. All this is in spray cans. So wait a week and cut and buff by sanding with 1200g wet then buff with woolen pad and compound then polish. Hope this helps.
CSM