WTF with this brake pedal
 

W123 with 2 solid inches of mush at the top of the brake pedal travel before any pads hit the rotors solid at all
I've pre bled and reprebled ad nauseum, used the reverse prebleed (inject B fluid into master with a large syringe) at output port, no way jose
I've got 3 spare new or rebuilt master cylinders here in boxes tried each one not a bit of difference
rebuild LF caliper, one piston was frozen, helped make braking better still got the hellish 2 inches of nothing.
got one of those nice brake fluid pressure bleeders, of course didn't help a bit.

Anybody got any ideas?
Even called the Continental German M. cylinder maker, got the run around.

Are bleed nozzles at to top on the calipers. I've seen a 190 where the rear calpiers were swapped which resulted in not being able to get all the air out of them.

been there done that
 

A very good point

I did it once

at least I learned about that

had to pressure wash the walls after due to the "ATMOSPHERICS" (it stuck to the walls, kinda yellow brown residue.)while figuing that out.

Check the condition of the rubber hoses to the calipers. If these are old, they may be expanding when you push on the brake pedal, causing the mushy feeling.