I've dealt with corrupter maser databases before - Instead of rebuilding all system databses, which is the fix for master db corruption, I did the following:

Took a previous backup of the master DB, restored is as a user DB on another server, took the MDF and LDF from the restored master DB and replaced the corrupted master's MDF and LDF with those - That worked quite well.

That way, you don't end up having to rebuild all system DB's and then restoring.