OH For Pete's Sake! 
I did a post-mortem autopsy on that brake line and found out that the culprit was that stamped bracket that secures the line to the strut! (see pic at beginning of thread)
The corrosion on that bracket grew to such a thickness as to increasingly clamp down on that section of hose, finally virtually pinching it off altogether.
I figured since the hose was "shot" I'd do a destructive autopsy... tried to run a wire through it but couldn't; cut off hose where wire stopped going in and from either end it stopped right at the bracket. Pried the bracket open (AFTER both ends had been cut off) and Voila!- hose opened right up.
Would I have had that knowledge before I could have pried the bracket open without even removing it from the car. I wouldn't have cut up a perfectly good hose and I wouldn't have bought a replacement and did all that work to install it either. So when the passenger side starts doing it I'll know what to do. Actually, I'll be proactive and go pry it open a little bit right now.
In all the ridiculously excessive online research I did for flex hose failures I did not come across this as a cause at all.