Clutch issues, maybe an internal leak in slave or master cylinder

Ok so I have a 2013 Prostar with the 15L Maxxforce. The issue I'm having is when I'm stopped at a light or backing the clutch engagement point changes like to the point that the truck wants to take off as soon as I move my foot at all. And if you just rest your foot in the clutch pedal with it out of gear the pedal fades like air in the system. Can't find any fluid leaking and the fluid level never changes. Bled the slave cylinder and didn't seem to see any air in the system. Could the master or slave be leaking internally like a brake matter cylinder on a car?

 

Do you suggest just replacing both and do a system bleed?