Well, I went ahead and replaced the four capacitors in the vertical section as recommended by Don and others. Also checked the two resistors mentioned and they test within spec. Can't see that it made any difference.
I may have to build the K5 couplate next...
I suppose the rest of the main board caps should be changed first.
But, another problem has started which has been getting progressively worse. Periodically the set will lose all horizontal output momentarily.... The picture collapses and then immediately starts to come back. When this happens, I hear a "click" sound from the high-voltage cage, presumably from the flyback transformer. I've tried watching carefully when this happens, but can't see any arcing, just the the "click". Started out only happening once or twice in a troubleshooting session, but now it is about every 15-30 seconds.
Does this sound like a flyback problem?
Thanks for all of the suggestions so far, I really appreciate it!
Wes