Super Mario Galaxy - Broken Disc

[Antwan]

I've had this problem for quite a while now. In Super Mario Galaxy, when I play Luigi and go to fight Bowser in the final showdown, everything runs fine. I beat him without a sweat and see Luigi and Peach holding hands as they touch down on the ground. However, as soon as it shows Bowser's planet exploding, the game freezes up and says the disc cannot be read.

I take it out and put it back in: nothing. I played the level a couple more times to see if it was a one-time fluke: nothing. I cleaned the disc with pure water and a cloth: nothing. I'm at a loss and because of this, I never beat SMG 100% despite owning it for 5 years.

What do I do?