Any vehicle which uses hydraulics for clutch actuation needs maintenance over time. Nothing more than a preventative maintenance issue.
But you are talking about a vehicle that is more than forty years old! So the entire system must be rebuilt. New and reconditioned masters and slaves are available as well as service kits for each. There is no hydraulic system any simpler than a Scout 80 clutch.
And once the hydraulics are functional, you will discover that the clutch throwout fork and pivot point is most likely worn beyond use, so those parts must also be exchanged, along with the throwout collar and the throwout bearing.