Why didn't Harry use a repairo spell on some of the books. He forgets that he can use magic. Oh well maybe he will figure it out sooner or later.
Author's response
I'm taking the position that the lack of magic being used is so they don't attract Voldemort's attention while in the castle. I also look at it along these lines, most of the books are beyond repair; quite literally rotted away to nothing or been eaten by pests over the years. My view on the Repario charm is you have to have something to start with, and unfortunately in the time that they had, they didn't find much. This doesn't mean that there isn't anything salvageable in the castle, it's just not in the Library.