3.5 v8 classic 5 speed

The clutch on my Range Rover slips really bad. I did a basic test before in 4th gear holding the brakes with a tiny bit of revs and it stalled. However today I went up my half mile long farm track and it just slips constantly. The engine revs like its in neutral, I held the brake when moving and accelerated and the engine just revved no movement.

The hydraulics are at least 5 years old and one thing that's rather odd. Is after prolonged use the clutch won't disengage, there's resistance on the pedal but it won't go in any gears then after leaving for 5 minutes it's okay. The other odd thing is you press the pedal about 90% of its travel and the clutch disengages then in the last 10% of pressing to the floor it starts to engage again.

So I'm looking for diagnostics on this one really, after doing numerous clutch tests the day before the clutch itself appears to have life left in it however today it's just slipping and not engaging or disengaging properly.

Would the slave and master cylinders cause this or is it time to rip out the gearbox?
I don't want to take the gearbox out to find the clutch still has a lot of life in it.

I would be looking at all your servos and pipes first as pipes do fail without looking as though they are leaking, there is a word for this but I'm having a mind blank.

If it's slipping it's buggered.
Hydraulics hold the clutch off but can't make it slip unless it's Jaming which I think is unlikely.