I clean all my DS games with products from ebay seller "The Nerb". He sells a liquid called classic game cleaner and hands down cleans out more deposits and what not than your traditional alcohol. Also Nintendo Repair Shop .com sells cleaning products that work most excellent. The cleaning paste and rinse have served me well. In fact on all my 2600,7800,colecovision,n64,snes,nes,genesis,neogeo....etc...etc. cartridge games......I take them apart. I then use the paster then rinse and my games are flawless. I do regular maintenence with Classic clean from the Nerb. The result.......no matter how old a game.....it works the first time. Does this work on DS games you ask??? Well.....my girlfriend has been speniding long hours on Harvest Moon DS. I took the game out and found the black stuff starting to develop on the contacts. Cleaning paste on a q tip, followed by rinse to get off the excess and its a brand new game!!! If you need any links to the above products.......shoot me an email and will galdly help you out.
P.S. I also make quite a few extra dollars cleaning so called "Broken Games" in the area i live. Havent had anybody disappointed yet.