I am running out of patience. My car has some crud stuck on the black plastic area directly under the doors and on the fenders and it's quite visible. I can't get it out. I washed it twice and no difference! I'm afraid to use a plastic bristle brush because I don't want to scuff it and make it worse. What do you use to get the dirt out of the plastic?

 

boar's hair brush comes to mind.

 

Post a pic of it so that we know what you're dealing with.

 

yeah - depends on what the crud is. Tar? Then use tar remover or WD-40 and it will desolve right off. Re-treat the plastic with Black Wow, 303 or whatever when you're done.