As I am almost the last remaining user of CDs, this may not be of much interest to other music fans, but I have been using the remainder of a product I bought perhaps 25 years ago in the UK.
BIB CD polish is used to deal with ingrained dirt and small scratches on the surface of CDs. The 7 ml bottle has lasted so long as I use only a single drop for each disc (and I try to not acquire many damaged discs!). This usually works. As far as I can find out, it’s still available.
I also found a video on YouTube of a guy using Brasso to polish lightly scratched discs. I’ve tried it on a rough disc that now plays perfectly. It’s crucial to rinse the disc with warm water after polishing and buffing to remove Brasso and dirt residue. Brasso will polish any kind of music, not only Metal!
UPDATE 12th June 2019: what I really like about polishing faulty discs with Brasso is that it works! Unplayable and sticking discs play perfectly after making them shiny by removing the tiny surface abrasions and scratches.