I have had an experience with the brakes. Some of this might help.
One day I was braking normal and the pedal was 'hard' at the top(
before pushing on it); you can bleed either side of the front and
back to normal for about 10 stops and 'hard' again. Disconnected
the abs sensor on the diff(10 min) and plugged back in and went
back to working as it was designed.

Now I have to go all the way down to brake. Replace the booster
because of age but did not help. What would be rational without
replacing parts on a hit or miss?

 

The flexible rubber brake lines rank high on the suspect list. Sometimes the internal walls of the hose start deteriorating. When this happens a piece of the rubber can act like a one way valve allowing fluid to flow to the wheel cylinders (or calipers)but not back again. Well at least not quickly, which is why if the brakes are left alone for a bit the pressure will slowly bleed off. However, in your case you said that you can bleed either front wheel and back to normal you go. This kind of rules out the hoses. This brings you to looking into only components common to both front wheels. Things like the proportioning valve, the ABS valve, or the master cylinder. The MC is the least likely of the three and the ABS valve is the most likely since it can hold pressure if one of the internal solenoid valves is sticking.

The reason you now have to go all the way down to brake is likely due to air having been sucked into the calipers when you opened the bleeder screws.

 

brakes were bleed by mechanic and stayed the same.
(mechanic said have to start replacing the MC, Por
valve etc.)
One day later I pumped up the brakes and put a stick
to hold the peddal down. I cracked open the proportioning
valve and it blatted(air)and a little fluid. Close that up
and drove for a day. Brakes came back(started working)
and lights turned off on the dask?????????
Anyone have an idea of what happened?

 

I think Alloro had mentioned it ...

"...The reason you now have to go all the way down to brake is likely due to air having been sucked into the calipers when you opened the bleeder screws."