Is it definately the clutch slave cylinder gone ? Because the clutch master cylinder is the common fault on the 56 plate and above, and its the least hassle to fix.
Having mine done at moment, my symptons were the clutch pedal wasn't coming right back up on its own, the last inch you had to pull up with your toe.
Master cylinder £22.00 from vauxhall and fitting £75 from one of my customers who is a mechanic.
If it is the slave do the clutch while the gearbox is out, it extra but it will be worth doing.
Darren