To those that posted in this thread....
https://www.pentaxforums.com/forums/14-general-talk/313180-reckon-what.html ......I thank you and appreciate your responses. Some of you were right on target, and though it could have been a number of things it did end up being a leaking wheel cylinder that was not so evident at first sight.
Anyhow...that is just the beginning of the story, unfortunately.
I took it to my regular repair shop, a certified shop and the best in town. I've had a ton of service performed there over the years, always first class. I know the owner and the mechanic I use most often is very talented and dedicated to excellent service.
They are well known for meticulous service at fair and reasonable prices.
They made the repair and installed new rear brakes;;;the front were fine. Yesterday afternoon they had it ready and I picked it up just at the start of rush hour traffic, which is very here on a Friday afternoon. As I drove away I heard a little noise that was not familiar, but assumed it was not abnormal, just the new brakes "settling in" or something? As I got down the highway a few miles it became louder and more frequent .....then some vibration. I got out wondering if I had a tire going flat, but after a quick glance I could see they were all ok.
Turned around and headed back to the repair shop...got within two blocks of it when there was a sudden "thud" the rear end dropped, and my left rear wheel passed me in the oncoming traffic lane. I drove it over onto the shoulder, dragging the rear hub in the pavement and got out and retrieved the wheel. Amazingly, ther was a brief lull in traffic in both directions just as this all transpired or it could have been a real catastrophe. They drive wicked and fast on that road on a Friday afternoon.
No one killed, no one injured. Now it's up to the shop to make it all right, and I suspect they will without me having to get nasty. They are good people.....I kept my cool....didn't go ballistic, I was just thankful no one was hurt....and you can bet they were too.
You're just going along on a beautiful sunny and warm day in the middle of February, life is good, all is well.....and then it isn't.
Stuff happens....no one is immune.
I had some bad luck....but the good luck outweighed it by miles...and maybe someone's life.
Best Regards!