Hello,

 Summary: Unknown source of air in front brake circuit.

Solution: It turned out to be the brake light switch.  Yes, it really acted
          like a check valve: no fluid leak under positive pressure, leaked
          air in under negative pressure.

          Hindsight says that that was the original problem as well, and I
          never needed a new master cylinder.

Thanks for all your suggestions.

Mike

Michael A. Radtke  -  Z74               Voice: 602-862-4897
Bull                                      FAX:         4853
13430 N. Black Canyon Hwy.
Phoenix, AZ  85029                      Email: m.radtke@bull.com