Rear Spoiler on 3 door / convertible - a trick
These spoilers are made of a foam type substance with a thin rubberized outer coating. If your spoiler is degraded physically so that the rubberized outer coating has decayed, you're kind of out of luck, but if its just faded and not - black looking despite attempts to protect/treat it, i figured out a way to make it look great. PS. Some spraypaint the spoiler. Big mistake in my opinion, it'll crack. Eventually. Or very quicly.
Here's how I did it... it works brilliantly. I'm incredibly picky too... I learned this on a Porsche BBS where they all have issues with rubber lips on certain vintage 911 whaletails.
1) Clean off the spoiler with something like All Purpose Auto cleaner, disk soap/water, something without protectant. Don't use simple green, it's too harsh here methinks.
2) Get a small container of KIWI LEATHER SHOW permanent black dye. Not show polish, but the actual black leather dye that comes in a little bottle for like 3 bucks at the store... it has a foam applicator tip.
3) Wait for the spoiler to completely COMPLETELY dry. Bone dry. Otherwise it'll streak. I then ran a wide painters masking tape around th espoiler where it touches the car.
4) Using the foam applicator fairly liberally put the kiwi black leather dye on the spoiler. It'll soak in pretty quick... Maybe give the thing 2 coats over all.
5) Buy 303 Aerospace Protectant. Do not use armor all, or anything like that. 303 Aerospace is hard to find localy, I buy it online for maybe $15 a bottle... trust me, it's well worth it.
6) When the dye has dried... apply 303. I reapply it about every 2 - 3 weeks when I wash the car.
My spoiler on the grey 89 SPG looks like brand freaking new now, and has for over a year, parked outside about 50% of the time.
The dye is great because its water based, and really thin. It doesnt cake, etc... and it'll actually cover up those whitish spots on teh spoiler from old wax or environmental fallout.