now that you mentioned it the old MC seemed to be leaking where it mated with the booster. it was only enought to bubble up the paint and then cause the booster to start to rust. it was a very slow seep and didnt cause much fluid at all to leave the system. I figured when I changed the MC this would stop that leak and so far it seems to have worked. Could that leak have meant for sure the old MC was bad and caused air to enter the system? If thats the case then the new MC should be good and it sound like i need to rebleed the system once or twice and see what happens. I just cant figure out why it doesnt happen all the Time. I would think if there definitely was air in the system it would happen all the time.