Yep, slave or master. Check the slave first perhaps, by peeling back the dust shield, where the thrust rod protrudes from, then the same with the masters rubber dust cover?: Looking for fluid of course.:
I'm ashamed to admit Mr Clutch replaced the slave or master cylinder (can't remember which) on my old 156... I wouldn't recommend them again although they were cheap at about £300... that was about £250 less than my local Alfa specialist.