I've previously had great success with Forever Black on a BMW, and the BMW folks swear by it - it is a dye not a cleaner: foreverblack.com.

I have the same problem with the trim below the windshield fading but have yet to try Forever Black on it... was going to see if the dealer will replace first, since they've been really helpful with my other trim issues.

Of course, I also have a sneaking suspicion that Forever Black is the same stuff in the dye you use for shoe edges, but that's just me.

I bought it from a BMW parts site but I know Autogeek sells it as well as other places (Griot's even has their own version too).

If my dealer won't cover the faded trim I'll post results, but it may be a couple of weeks.