spongy/non existent clutch

96 2.5DT Manual Rangie, 135k miles.

recently some mornings i have no life in my clutch pedal. i turn the engine over, leave it a few mins then feather the clutch for a minute or so, and low and behold i can select a gear. it is fine when im driving, and only when the engine has cooled down do i get the problem again.

i am not losing any clutch fluid, its been at the exact same point on the max line for months. dont seem to be any holes/splits in hoses.

any ideas?

Could it be the slave cylinder? In a 94 Discovery I had it was close to the transmission and the inner o-rings were bad, so it wasn't holding pressure. It is repaired sort of like a master cylinder for the brakes.