Hi Sam
Welcome aboard to the forum.
Try the cheapest fix first and make sure the adjustment is correct at the pedal box and changing the fluid like JC said is a good idea.
I had a problem like your Land Rover suddenly loosing it's adjustment and the most probable explanation was that my slave cylinder push rod wasn't seated properly into the throwout race lever and over corrugations it found it's way into place, upsetting the adjustment.
Thinking the worst, I pulled my gearbox out to find there wasn't a thing wrong with the clutch apart from some normal wear. :(
Since I had already brought a new heavy duty clutch and pressure plate kit, I fitted those new parts along with a strengthened lever back into my defender and used the best of the old parts in another rebuild ( 'Fred' ).
By the way, I didn't changed either the Defender's master cylinder nor the slave cylinder at the time and they are still working fine.
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