Slave Cylinder/Clutch Return Cylinder Problem

I've got a problem, and I'm stuck, so hopefully I can get some help (and some good news!) I've got a '91 Cherokee sport that is losing pedal feel and pressure. It's the 5-spd, 4x4, inline 6. Mechanic says the slave cylinder (aka clutch return cylinder) is bad on it, but that unit has already been replaced once on this truck and it's only got ~150k miles on it.
Basically, if you put fluid in the master cylinder resovoir, the clutch will work fine for a while. In 15 or so minutes, however- and especially when the Jeep has first been started- it will become difficult to get into first gear, reverse, and finally the clutch pedal will just go completely dead. It doesn't seem to be losing much fluid, just a little, and I can't tell exactly where it's coming from. Doesn't look like a problem on the master cylinder, fluid spray seems down by the transmission housing. Unfortunately, the slave cylinder is internal, so if that's the problem, I'm screwed. I'm hoping it may just be a cracked hydraulic line (from the master to the slave cylinder) but I'm not sure, and don't want to spend money to buy parts until I have a better idea of what's going on.

So... what's wrong with this pain in the ass hydraulic clutch system?

and WHY did anyone ever think this was a good idea? Overcomplications SUCK! :mad:

if the fluid is leaking out off the bell housing then it's a safe bet that you need a slave cylinder.