Tried polishing the disk?
I usually start with a baby wipe, and if that doesn't help, work my way up to car polish.
I'm amazed at how many music CDs I've saved this way (Never had to do it with a game CD, but I imagine the principle is the same).
If nothing else works, you could just do a hail mary and mail the whole set to Ubisoft.
Miracles can happen.
Better yet, I see Amazon has the whole thing for $6.68
with super saver shipping.