The Mag 21 was Rock Shox's high end fork for a while. I would have to say that you'll be much better served with a new fork for the bike for a variety of reasons. For starters, a lot of the problems that surfaced 5 or 7 years ago with forks have passed. They are generally more responsive to rider input and easier to tune for your riding style than the older ones are. But, it's also really difficult to find parts for them. If you blow out a seal or the cartridge inside the fork (if memory serves and your fork has a cartridge to blow) it will be very difficult to find replacement parts. I have a 1996 Judy FSX, the carbon version of a Rock Shox fork that was made for Specialized. I recently tried to see if I could rebuild it, but came up pretty short on the parts end of things.