I tore into it this morning and the only thing I really came up with was the caliper/pad slides were pretty corroded and dirty. I pulled the caliper and found it was not binding or froze up, so I cleaned it up and flushed the brake fluid. I pulled the brake hose and hard line up to the proportioning valve and found nothing corroded closed or kinked; both the hose and hard line was free flowing. I cleaned and lubed up the caliper/pad slides, reinstalled everything then flushed and bled the system. Took it for a long drive afterwards and no problems; guess it was just the corroded slides. And yes Jim, you are right, if it comes back I'll be installing new calipers on it.