Thanks fellas ...

After I sent my post, I pulled the driver-side rear lamp and took it apart, looking for any visible problems. I really didn't see any, but now that I reinstalled it, all the tail lamps and brake lamps are working fine! Perhaps babymog was right, there may have been a ground fault that was corrected when I reassembled the lamp. I drove about 10 miles and, so far, nothing amiss.

But just in case Macdrone's idea is possible ... are you referring to the blocky relay that sits north of the under-the-hood fuse box, near the cowl? I replaced that bugger about two years ago -- it was the culprit in a lot of problems I had with turn signals. My turn signals would work fine a couple of times, then peter out. I'd reset the hazard switch and they'd work fine for awhile, then blink slowly, then cease altogether. Really weird: this happened only on hot humid days; they were fine in the winter. Anyway, I discovered on this forum the $75 relay that, once replaced, cured all those problems.

So ... for now ... I'm keeping my fingers crossed ...