Two thoughts - don't you have something more important to worry about ??? -
lol ! 
Just joking.
I have that problem too, and I keep about 150 car restoration products
around.
It gets into the plastic.  - physically remove the surface it seems, like
with sandpaper, and we don't want to do that of course. 

Trying to think of how to liquefy the brake dust to pull it out of the
plastic ............
I have some pretty beat up ones. I think I'm going to try brake fluid, and
perhaps tire cleaning fluid.  Even lighter fluid or diesel fuel.  I have
like 10 and some of them are really almost dead, so I can experiment without
risking anything.  They used to cost 65 bucks each new at the dealer.   
  I also get spray paint at hardware stores that is specifically for
plastic. Sticks really good. But doesn't come in silver or silver-gray and I
wouldn't want to tart up the hubcaps either. I can do them in white, blue,
or bright green though. the paint is called 'fusion.'  Just joking. 
 I clean them as best I can, and leave it at that. I scrub with an old
toothbrush too.
Scott
www.turbovans.com 

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Michael Sullivan
Sent: Monday, January 14, 2008 2:42 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Clean my Dusty Caps

What can I use to get the brake dust off my plastic hubcaps on my 91GL? I've
tried brake cleaner, carb cleaner, orange glow, palmolive and still have
residual. Don't want to remove the finish.  Thanks, guys.
  Michael
  91GL 'Gringo'

Thanks, Michael Sullivan