You're getting air in the system and do not assume it's the master.
Try this. At the brass cross block, disconnect the brake line to the rear
brakes. Find a suitable sized bolt to block off the hole (wrap some Teflon
tape on it).
Now you have a simplified brake system with just the front brakes. Bleed it
and report back to the list your results.
IMHO, Silicone brake fluid is the best thing that ever happened to
hydraulics. But I don't want to revive the holy wars..
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