Cusser
+1y
Likely best to replace both clutch master and clutch slave cylinders (unless there's a leak in the lines, as Dat Dood stated). I've had this happen on mine, and so have others. In the 14 years I've had mine, I've had to replace these parts a few times, so I'd recommend life-time warrantied parts.
Tips.
Bench-bleed the clutch master cylinder before installing.
Use a flare wrench for inital loosentin and final tightening of fittings so they don't round off.
Loosen the line from the clutch slave a little BEFORE unbolting it from the transmission (and the reverse when installing).
Bleed out ALL the old dirty clutch fluid (brake fluid) wheen bleeding so no old fluid remains in the system (don't let the reservoir go dry, keep topping it off as necessary).