GR-40 trim cleaner topped with a coat or two of Opti-Seal has worked great on all trim and exterior plastics for me. Seems to last a bit longer than 303, Vinylex, etc...

 

my preferred choice as well. For that matter, anything poor boy's makes is excellent and very inexpensive!

 

I permanently restored the cowl area on a previously owned Mazda. Here's how.

1. Remove cowl carefully. The plastic is actually pretty soft and will show marks easily
2. Clean with residue free cleaner
3. Duplicolor adhesion promoter (follow directions on can)
4. Duplicolor Bumper Coating (approx. 3-4 coats)
5. Reinstall
6. Marvel at perfect looking cowl

Pictures:
Before - You can see how faded it was


During -

After - Plugs to cover screw holes not reinstalled yet. Also resprayed the wiper arms with paint while I had them out.

 

It's very expensive, but a product to consider is the Ultima Tire & Trim Guard Plus. I cannot attest to its durability, but they advertise it as lasting a couple of months. In a recent thread on Autopia a couple of folks have confirmed this claim.

I just applied it to my Stewie's cowl and trim. It really did shine and darken up the cowl. UTTGP does have two downsides: First, as I said, it's expensive. You might wait until Autopia puts it on sale again. Second, it comes out of the bottle too quickly. A little goes a long way. They need a better bottle and application system.

But if it lasts 2 to 3 months, then it really is worth it.

+1 also for Meguiar's Trim Detailer. It really does work well. I have gotten more than a couple of weeks on both my S2000 and my wife's (now sold) Taurus.

 

This is stuff is amazing.

Quick coat on the black trim for a 996TT and it restored it as if it was new. In addition, was used on a Mini Cooper S that needed TLC. After the application it appeared as it would from the factory.

Serious

The Poor Boys products in general are a great buy - great results, low price.