It seems that the vigorous pumping of the brake pedal during our attempts to re-pressurize the cylinder and lines caused a rear circuit internal failure of the seals. Suggestions for next time would be to be more gentle when working on bleeding the brakes.
After an attempt to pressure bleed the entire system , the mechanic reported a master cylinder failure precipitated by over pumping of the pedal while the system had little fluid in it. So, a new master is on the way.
And still no car for another 3 days.

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1984 300D