Drove for a while on a warm day and the clutch stopped working
 

It is a warm day today, and I drove the FC around for an hour at lunch just to run some errands. No hard driving, a mix of freeway and surface streets in thick lunch-time traffic, and the engine temp never got above normal . As I was heading back to the office, I noticed the clutch pedal was getting soft...a lot of freeplay at the top of the stroke before the clutch would disengage to shift gears. Just as I got to the parking lot I noticed that even with the pedal all the way to the floor, the clutch wasn't completely disengaged with the car in gear. I pulled into a parking spot and put the car in neutral, and then couldn't get it back into any gear at all. I let the car cool off for 45 minutes and without starting it, I could tell that the clutch feel was back to normal and I was able to get the tranny into all of the gears.

I don't see any leaking around the master or slave. The fluid is at a normal level and hasn't changed level, and I have a braided stainless line between the hardline and the slave.

It seems like a heat and hydraulic related issue. Any idea what could cause this, and what I could do to fix it? Is my fluid just old and needs to be replaced? Could it be that the heat is causing a problem with the master and/or slave and maybe a rebuild would help? I should be able to drive my car for more then an hour during the summer.

Check to make sure the master isn't leaking to the inside of the car. Does the peddle get stuck down? Could also be broken pressure plate.

I just went outside and checked. Nope, no leaking inside the car. It didn't get stuck at the floor. It was just spongy at the top of the pedal stroke when it was hot.

Might not be leaking, but your seals may be bad within the master. Try and replace with new fluid/bleed the system and try to replicate the failure. I think yur master internally failed though.

Would it be a normal failure mode for the seals in the master to act like they are failing only when it is hot, and return to function after it cools a bit?

Hot and cold, expansion and contraction. If it's 25 years old, better believe it will do odd things

mines doing the same thing with the warmer weather, and I recently replaced the master and slave, but, I also replaced them with o'reilly auto ones, think it may of been a mistake

a weak and swelling rubber hose between the master and slave can do the same thing