[Tommy]

For those of you who may be curious, I'll expand on my comments about the geometry of the clutch shaft affecting the life of an aluminum master cylinder. The clutch pedal moves the shaft that presses against the piston within the master cylinder. If the shaft pressed precisely perpendicular to the piston (parallel to the walls of the master cylinder) there should be relatively little wear on each stroke, and the wear would be even around the entire piston. In actual practice, the end of the shaft connected to the pedal swings in an arc, resulting in something other than precisely perpendicular movement. Ideally, the shaft should be perpendicualr to the piston near the center of its travel on each stroke. On my car, the shaft was connected to the pedal at a point well below the centerline of the master cylinder. Consequently, on each application of the clutch, the shaft was pushing both in and up on the piston. I believe this tended to cock the piston in the cylinder, causing rapid wear on the top and bottom of the cylinder. This was confirmed by measurements of the leaking cylinder bore. ... I tried to align the clutch shaft by moving its attachment point higher on the clutch pedal. But this reduced the effective throw of the shaft and would not allow the clutch to fully disengage. So, I abandoned the softer aluminum master cylinder in favor of the CNC steel one.