3m Bondo Restore Black. Bought a bottle with applicator sponge at a pep boys for 10 bucks. You can find it online easily as well. I have painted flares, but I used this on my bumpers, fog lights, mud flaps, side steps, gas fill up surround, taillight pieces, etc. anything black. It works incredibly! I can't recommend it enough. I had tried black to black last year. Was not impressed. This 3m product is so easy to apply and the results last for a long time. It's kinda like a solvent with black dye in it. Strange thing is that it is not sold in the wash,wax, and restore products section like black to black is. It's on the shelf with DIY rhino linings and products like that. Like I said, I didn't apply to black plastic fenders so I can't guarantee it will work on them. But it works awesome on every other piece if plastic.