[FRED/LI]

Bleed the clutch slave cylinder on the top of the tranny/clutch housing. That may do it.
More likely, replacing the cylinder is necessary.
These seem to lose a little capacity when hot from exposure to the engine heat.
One remote possibility which could be easily checked with the floorboard off is the roll pin holding the clutch pedal. Hold on to the plunger arm and move the clutch pedal by hand. If there's slack in the movement, the roll pin may be failing. Been there twice.........