I had an AFCO die in 2300 miles.
I just started to bypass the piston slowly. (I was hoping it was not the McLeod hydraulic throw out going south since I had just put a new engine in!
) I did not see any part any particulate matter to speak of, at first. I had drained the master cylinder out completely into a container and after everything settle out, there was some extemely fine black particulates in the bottom. I opted for replacement. Now that you have mentioned the need for perpendicularity, I guess I had better check it out. I only have a few hundred miles on the new unit.