i have a '73 and i've replaced the clutch slave several times. it will drive good and strong for about an hour then the piston is forced all the way forward, sometimes nearly out perma-clutching (forcing the yoke forward, jammed) until i can get under there to unbolt it. even after removal from the line the piston wont go back into the unit. i now keep an extra slave with tools in the car just in case. good thing they are just $12 a pop. is there an adjustment i am missing to lessen the pressure?