I had a problem recently where i would lose my clutch pressure after driving long distances. It would always come back after everything cooled down. my issue was having water in the system that would heat up, expand, cause air bubbles, and just make the whole system die.
I fixed this by flushing out all of the fluid with new fluid. Put a tube on the bleed into a jug and crack the bleed so it only bleeds when the peddle is pumped. fill the reservoir and proceed to pump the clutch 3-4 times being sure not to completely drain the reservoir. I probably went through half a quart to 3/4 of the DOT fluid after i was done and i have much better clutch pressure than i ever had.
Still have to take it on a long trip to see if i got all the water out... but definitely better. I would start with that before going with the full replacement.
Colorado Jeep Club Member #286
89 YJ 2.5L
OME 36R's, Bilstein 5100's, Bserk 5/8" shackles, 33x10.5 BFG's on 15x8
09 KK Sport 4X4
235/75/16 GY Slnt Armor
CB 2' Firestik