GameCube disc are the most fragile lil buggers, next to Dreamcast disc. Very thin layer compared to any normal CD or DVD. Ironically, UMD's are made the same way.
Do you own a dremel by chance? If so, they usually have a little buff pad thingy which you can put on and basically buff your own disc. It really works great if the toothpaste won't do the trick.
GameCube disc are the most fragile lil buggers, next to Dreamcast disc. Very thin layer compared to any normal CD or DVD. Ironically, UMD's are made the same way.