This is an old thread but I'm hoping someone is still out there. I am having this same issue with the front calipers not bleeding on my '83 300d. Replaced the master cylinder and bled the rear brakes the conventional 2 person way. Got to the front, can't get anything, crack open the bleeder and the pedal doesn't move, no fluid flow, my head spinning. I saw that the starter of this thread managed to get theirs to work, I am desperate for help!