I use something called Novus to clean the plastic ramps on my pinball machine and it works great. Heres an eBay link, or just search Novus.
http://cgi.ebay.com/NOVUS-1-2-3-pinball-cleaning-kit-Scratch-Remover_W0QQitemZ102250406984QQihZ010QQcategoryZ13727QQrdZ1QQcmdZViewItem
Kevin
