I've been using this method for 12 years now, both at home and at work (I'm chief computer geek), and am still using the disk I recovered 12 years ago without further treatment....
(If the disk is visibly scratched so that you can see the scratch on the top, nothing will help, so stop reading now.)
Rinse any dust, etc. off with lukewarm water and dry.
Take a bottle of Rain-X and put two DROPS on the bottom of the disk and with a cotton ball, GENTLY (ie - no pressure) evenly spread the RainX drops around the entire surface of the disk. Lay the treated side up and let dry for 20 minute - it will become a nice dry haze. With your cleanest, softest, wornout, 100% cotton t-shirt buff off the haze, again, no pressure. If you have any lint that won't blow off, you still may need to let it dry another few minutes.
The RainX fills in the cracks and does a decent job of restoring the surface. I use this for all types of music and data CD's and CDRs and have had pretty good success in recovering disc's with it.
Again, rinse first and DRY, and a little rainX goes a long way.
If this won't get it, you are likely to have to use SetMenu's idea of polishing the surface (they make restore kits that do this) but I would try a none abrasive method first.
Good luck