If it's the self-propelled clutch on a front-wheel-drive M4, forget new parts - they haven't been avalable for many years (15 at least!).
Best bet is a working replacement gearbox - they do come up for pennies on ebay occasionally.
If it's a newer version, come back here and I'll advise.
phil_saunders(a)bigfoot.com
Phil Saunders, April 2009
