Replaced only the Clutch Master Cylinder. All is well so far. Hose from Master to Slave was re-used. New clutch master cylinder came with a o-ring rubber washer and a roll pin - the o-ring goes onto the hose. Not just into the master cylinder hole. When you do it wrong and force the hose into an opening where the washer is sitting, it cracks the washer and you have leaks.
Hopefully this is helpful to C5/C6 owners