I don't think that the disk is the problem unless the DVD player its self has a burned out motor and is not spinning. I 've put some really scratchy games in my xbox and they played fine. So its unlikely the problem.
I believe the problem is a conflict between the the Y: partition and the plot numbers in the auto-save. <--- "One Dak Vesser theory"
What koTOr II is doing is storing all the current data into the Y: partition.(Just like Kotor1 did) Files like all the .2da, TLG.erf and muisic files going into a folder called "Cache/Dataxbox". So when you load into a new area (like out the Ebon Hawk to Dantooine), the game will load all the files from the Y:/ Cache Folder and not the DVD.
Now sometimes durring a loadup procedure (due to some random glitch) there's a conflict between what 's stored in the auto-save, and what's stored in the Y: cache folder ( It could be a number of reasons--> corrupted memory, bad hash values in the load query, plot numbers, & so on). If that happens, the executable will then query the information from the Dvd as a failsafe. So when you see the load screen pop up, you'll hear the Dvd winding up, The right info is retrieved, and the cache folder gets partially reset, conflict resolved, load complete.
But for some reason, It looks like the KotOR II executable is comming up with some error when retrieving the info after query from the dvd, it's as if it can't respond back to its self and as a result you see this "disk may be dirty or damaged" Message <--"Another Dak Vesser theory"
I've seen this happen once on my xbox too. Dirty or damaged disk message showed up in the middle of a load;
After the cut scene with the Ebon Hawk Leaving the secret Jedi Academy on Telos, the game was supposed to loadup the cutscene with T3-m4's holo recording of the Exile's Trial and the HandMaiden joining the party
I shut the xbox off, took the disk out, turned it back on, put the disk back in, reloaded the autosave and it continued right into the cutscene where it left off. ---> everything was all good.
So I don't believe the disk is bad. It's just KoTOR II - TSL's defult.xbe is very buggy, twitchy and glitchy --> nothing a good update can't fix.
~Platnum hit DVD~
Try doing this: Start a new game from scratch so the cache can reset. If it does reset then you should be able to get the "gamesave in question" to work again.
If you can't get the "gamesave in question" to work again, then the save is damaged beyond repair.
If you try to start a new game but can't because of the "Dirty or damaged disk" message popping up, then the Y: Partition will need to be wiped clean, and unfortunately you won't be able to do that if your xbox is not modded. <--but this case is highly unlikely.
will I hope my theory makes all the sense in the world and helps. And "NO" I'm not a nerd!