I had this problem on my 1st gen... it took me 2 years before I figured out that it was my hard motor mounts... they were too hard and the torque from my engine was snapping up to 2 of them at a time. I dont know if you have solid motor mounts or moded ones but this was my problem. Also a leaky valve cover gasket leaks Alllll the way down to the front bolt on the tranny and heat, vibration, oil, makes it back out. Then the others fail...

Again I am not sure what you have done to your car but this is what happened to me... 3 clutches later... (1 stage 3) and 2 trannys... 40+ hours under the car.... it was the hard motor mounts... and the leaky valve cover.... Believe it or not...