Mark,

I am positive the problem is not at the bleeder screw.  And, I used a wrench.

Since my last post, two other things have come to light.

1) I think that I can test the master cylinder itself by disconnecting the
   offending brake circuit and attaching a hose to that master cylinder
   connection.  Drawing a slight vacuum on that hose must produce only
   brake fluid, and not air.

2) It was suggested that hydraulic brake light switches have been known to
   act as check valves.  I swapped these switches from my old master
   cylinder, so they are not new.  I can reverse their positions and see if
   the problem stays in front, or moves to the back.

Thanks for your thoughts,
Mike