Dull black plastic

Don't know if it's already too late for yours, but usually ArmorAll is great for cleaning plastic

 

Several products available such as AUTOGLYM's Bumper Care or Vinyl & Rubber Care, The Wax Shop, Bumper Black, Griots Garage, Bumper & Trim Reconditioned

 

I use Back to Black

 

303 Aerospace Protectant
Adam’s VRT
Einszett “Gummi Pflege”
Forever Black
Black Wow
Griot’s Vinyl & Rubber Dressing
Meguiar’s Trim Detailer
Poorboys World Trim Restorer
Car Brite – Bumper Kote
Stoner Trim Shine
Mothers Back to Black
3m Rubber Treatment
Smart Dressing
Lexol Vinylex

 

Are we talking interior or exterior? Is it originally painted or black molded color plastic?

 

Zaino All in One ?

 

+1 Mother's Back to Black works great.

 

If it is exterior black plastic and it is turning white or ashy colored then armor all, dressing, detail spray is not going to help it. It may look good for a day or two but will turn white again... Someone earler suggested Griots bumper trim--I have used that and it works well. It is almost like a paint but more forgiving if you get it on something other than the black... I did my lower rocker panel all the way around on my 328 a few years ago and it turned out great. Comes in a plastic bottle with a shoe polish type applicator...

 

Use a hot air paint stripper to heat up the plastic (not too much offcourse, or it will melt) This will bring up the black color of the plastic again

 

May sound odd, but a bit of peanut oil (or even peanut butter) rubbed onto the surface, let sit for a short while, then rubbed off will bring back the black and last a long time.

 

Using a mild abrasive and chemical cleaner (such as Klasse All in One or Zaino All in One) lightly worked into the surface will lightly "scrub" away the oxidized surface with the help of the chemical cleaners. The sealant in each product will seal in the clean look. I will post some before/afters of the difference on a 365 and a 328 with boxer paint on the bottom when I get a chance.

 

That will work on dried wax residue on plastic also

 

I love this stuff:
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Not knocking the idea but.....

Please post a picture of yourself applying peanut butter to your car

Seeing is Believing!

 

Given the current temperature in the suburbs of Chicago - I think the peanut butter would simply freeze right now. If it warms up anytime soon & this thread is still active - I'll take you up on that