ducati clutch

i've just bought a crashed '04 998. The bike has a broken clutch lever, no clutch pressure so I bled the line and change the lever but one problem it's losing pressure. If I pull the clutch i would pressure is there for about one or two second then the pressure plate slowly locking in on the clutch pack. I've changed plates,fluid on 996 many times this never happen. I'm thinking it's either the master cylinder or slave cylinder the is leaking. I've already check for leaks and there's none. Anybody knows why, any help is appreciate