I have a 69 with front power disk and put a used original MC in it (original). I had brakes that worked but they were low before grabbing. The rod is the correct length for the MC (deep bore). They suddenly got worse and I removed the MC and bench bled it again and then bled the whole system again. The brakes seem to sporadically grab a little when pumping and then I lose them to the floor again... Is this a bad MC? or could it be that intermediate valve that hangs from the Power booster/MC bolt (not proportional valve)? When bench bleeding, each port seemed to push fluid back into the reservoir ok. Are there any rebuild kits out there so I can keep the correct one installed if it is the MC?