Can you get it bled then the problem comes back after driving? If so, it's heat related and is probably originating where the fluid line leaves the slave and runs down to the body. It's very near the exhaust and coolant hose. It needs to be insulated with some good high temp plastic wire loom.
If you just simply can't get it bled, try my method. You will need a floor jack or you can run left front of the car up on a steep incline at a 45* angle to the incline.
Lift the left front wheel enough to get it off the ground.
Remove the reservoir cap and fill the reservoir to the top. Leave the cap off your reservoir and fluid container.
Go to the rear and open the slave bleeder valve until fluid starts to flow.
Using a heavy wrench or small hammer, tap the side of the reservoir 5 or 6 times to dislodge fluid stuck at the pushrod end.
Keep a watch on the fluid reservoir and when it nears empty, top it off again.
Repeat the tapping on the slave cylinder and observe for more air bubbles as the fluid is flowing.
Three cycles should be sufficient.
Close the bleeder as the fluid level drops to the FULL mark.
Test the pedal for release.
