Well, after giving all sorts of stretching exercises a try, along with cutting back my walking mileage to near zero, I finally made a vist to an orthopedic doctor today.
He wasn't especially worried about my sciatica until I told him about the loss of muscle strength on a hit-or-miss basis while walking. That loss of strength wasn't predictable at all and would just about buckle my leg when it happened and it was also painful.
Some quick X-rays were taken, and the news is that I have Spondylolisthesis, a condition whose symptoms include the slipping forward of all the vertebrae above one specific vertebra. My slippage is stage two out of five stages, and the distance the upper vertebrae moved is close to 7mm. That's a lot, I believe, and it seems worth worrying about to me.
Then the doctor scheduled an MRI. Once that is in, we'll decide what to do. Of course, Colette and I had already booked a hiking trek in Germany for June, so I just asked him if he believed I could do it. Much to my surprise, he said that a cortisone shot would make it possible. Wow, a doc after my own heart. LOL
Further down the road, most likely there will be some sort of surgery to fix the problem, like maybe soon after those hikes. :-)