I think you might find (if its the same as my vitesse) that the clutch fluid is drawn from the brake fluid reservoir.
I'm having a similar problem at the moment, mine is completely undrivable. Pedal just drops to the floor, bled out loads of air and it seems that air is entering the sysem somewhere, as the slave cylinder is under 5 months old im now suspecting the master cylinder is drawing it in somewhere.
Tom Poulton
November 2007