intermittent clutch issue please help

2007 jeep compass manual diesel. I keep losing clutch pressure have replaced the master cylinder three times and the same thing happens, the fluid is clean and free of any impurities. the pressure returns if I pump the clutch several times but then loses pressure without warning at anytime. Any suggestions?

2007 jeep compass manual diesel. I keep losing clutch pressure have replaced the master cylinder three times and the same thing happens, the fluid is clean and free of any impurities. the pressure returns if I pump the clutch several times but then loses pressure without warning at anytime. Any suggestions?
If you bled the system properly I would think the slave cylinder is bad.