Autosmart's ''Finish'' is a very good product for rejuvinating plastic and rubber trim quickly, will last a few washes before needing re-treating, expensive but a 5 litre pack should last you years.

Both exterior and interior use.

I remember seeing a vinyl roof (remember them) that had been scrubbed clean and then had shoe polish (the proper stuff out of a Kiwi tin) applied. Looked better than it did when it came out of the factory - and probably kept those pesky monkeys at safari parks from getting a grip on it.

Use peanut butter - seriously! Here's a video showing how to do it and how it works.

https://www.google.com/search?q=using+peanut+butter+to+renovate+car+black+plastic&oq=using+peanut+butter+to+renovate+car+black+plastic&aqs=chrome..69i57.34820j0j7&sourceid=chrome&ie=UTF-8#kpvalbx=1

I've read that (careful) use of a heat gun can bring back faded black plastic. You might want to try it somewhere inconspicuous first though!

That does work a treat ,the heat brings the oils in the plastics back to the surface but as you say you really need to be careful.

I use auto finesse "revive" but again care is needed, don't get the stuff on paint! I use 2 inch low tack masking tape to protect the paint, allows you get right into the edges of the trim, makes all the difference.

Meguirs Ultimate Black. Works on all plastics, leaves them looking like new.