S Max Clutch Hydraulics Problem.

Hi there I am a newby on this forum, and I am looking for an answer to a problem 07 Reg S Max 1800 tdci. Halfway through April the clutch failed stripped it and replaced the Dual Mass Flywheel/Clutch Assembly/Slave Cylinder. Reassemled and all fine until nine weeks later and the clutch Slave cylinder failed. Stripped again and replaced the Slave cylinder reassembled then the trouble started, the pedal would drop to the floor a quick bleed and away you go again, until the clutch pressure disappears again, then a bleed and away we go again. This was turning into about a weekly event, so five weeks later I changed the Master Cylinder, still the problem continued I then changed all the brake/clutch fluid for a higher spec and the problem is still there. There is never any leak of fluid which would appear to be the normal thing to look for. And the new Clutch worked fine until the Slave Cylinder failed which makes me point to the new Slave Cylinder but I can not work out how that can happen? Any ideas anyone.