Is the bleed screw at the top of the caliper (right and left side calipers not reversed ) so the air actually gets out when bleeding? It's happened MORE than once!
Could the master cylinder travel been overextended (into a previously untouched portion of the cylinder where it is rough) and scraped up the MC piston seal?
Booster problem shouldn't show up as the "foot to the floor" trick.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)