Why do plastics fade?
Plastic car parts leave the factory vibrant, however after years of being exposed to the elements the plastics begin to break down. The breaking down of plastics is mostly due to the harmful UV rays from the sun. Pollution in the air, extreme heat, chemicals and salts are other known reasons for the breakdown of plastics.

How do you prevent fade?
Park out of the sun avoid to extreme heat and UV radiation.

Does putting a layer of wax over the plastic help?
Putting a layer of car wax over plastic will only accelerate the fading process. The wax gets absorbed into the pores of the plastic trim and begins to accelerate the graying, chalky look.

What does work?
Nothing will bring your plastic trim back 100% to factory, but there is a lesser known but very effective option that is often overlooked. A 50/50 mixture mix of Boiled Linseed Oil and Paint Thinner will restore the vibrancy of the plastic as well as add a layer of protection. This solution is a good way to restore your OEM trim without ruining it with paint.

What is Boiled Linseed Oil?
Linseed oil is a natural oil extracted from flax seed. It is primarily used to preserve concrete and wood from deterioration. It is also used in many paints and wood stains. Boiled linseed oil can be found at your local hardware store in the paint section. Make sure to purchase the BOILED linseed oil, the unboiled will not be effective.

What is purpose of mixing it with paint thinner?
The paint thinner helps improve drying time. Japan drier or turpentine also works as well.

Downsides of using Boiled Linseed Oil?
It is not 100% lifelong preservation, you will have to go back and restore the plastic eventually. This may be every few years or every few months depending on the exposure levels of your plastics to the sun. Boiled Linseed oil is also not UV proof.

Do I need to prepare the surface of the plastics before applying the paint thinner and boiled linseed oil?
Yes, of course. Like any painting process, the cleaning of the surface is the most important part. It is the basis for the final quality of the applicant. If your surface is not prepared properly the renewing solution will not work as effectively. Clean the surface with a wax remover and or 91% alcohol.

Always protect the surfaces you are not restoring. Tape off around the trim or remove the trim completely to ensure no overspray or runoffs .

The process:
- Remove the plastic trim completely or tape off the sections of restoration.
- Clean the surface with wax remover or 91% alcohol (can be purchased at Walgreens or CVS).
- Create a 50 / 50 mixture of boiled linseed oil and paint thinner.
- Apply the solution using a spray bottle, foam brush or rag.
- Allow the solution to be absorbed for a few seconds and wipe away the excess.

here with pics https://forums.bimmertips.com/viewtopic.php?t=70