I have the exact same problem. Did you ever figure out what the problem was? I've raised the issue with Apple support and they gave me the same recommendation. I really would prefer not to have to reinstall the OS as that would mean a huge amount of time and hassle and possible loss of data or applications. And like you I would really like to find out what the underlying problem is.
A couple additional clues:
[1] when I log in as a different user, the problem goes away.
[2] Also, yesterday I reformatted one of my internal disk drives, though not the startup disk and the close parenthesis started working again for little while. Here's the details on what I did: The disk I reformatted contained lots of Quicktime videos and Final Cut Pro projects, which I temporarily moved to another disk while I reformatted it. After I reformatted the disk and moved the files back to it, the close parenthesis started working temporarily - but mysteriously when I pulled up iWork Pages documents I could not see the contents of the documents. The documents opened up normally and acted as if there was text in them but I could not see the text. I then opened and closed Pages a couple times and restarted the computer. Pages started working correctly again. I then worked on a Final Cut project and shut the computer down for the night. This morning when I woke up, the close parenthesis was no longer working. Unfortunately, I did not test the close parenthesis right after Pages started working again last night - so I'm not sure exactly when the problem resurfaced.
Have you figured out what might be causing this problem, or has anyone else out there?