Yer absotutely right, Jim. The problem occurs because the rotors are not running perfectly straight. Since these calipers have springs behind the pistons to hold the pads against the rotors, any axial movement in the rotors turns the pistons into air compressors, sucking air past the lip seals on the pistons, and into the brake system. You can bleed them till yer dead, and have a good pedal for a while, but while driving, with the rotors flopping, and pistons running in/out all the time, the system gets air back into it, and you get a mooshy(tech term) pedal that will eventually go all the way to the floor.
Some folks have resorted to removing the springs to keep this from happening(it does help, but it's not a long term fix), but the best "fix" is to make sure the rotors are running TRUE to begin with, and use the o-ring type pistons and seals.

btw..this really needs to have a new thread started, instead of piggy-backing on a really old thread.

I'm with the caliper seals sucking in air crowd.  That's exactly what happened with the '78 Vette I owned.  Your symptoms are the same as I experienced.

Thanks, guys! I'll get this information to the poor guy scratching his head.  I appreciate the help, and will start a new thread with the next problem.  You know there's going to be one LOL