First, my THANKS to all who offered advice, BUT.....

Figured it out all by myself. Checked the nozzles first. They were fine. The problem was interesting because the squirt failure would alternate between left and right sides. For a few days the left side wouldn't squirt; then the same would happen to the right. Sometimes both sides worked okay. There was never a total failure.



Obviously these symptoms eliminated electrical and/or pump problems.



On checking the T-connector that diverts fluid from the single hose to the two nozzles, I noticed that I could blow air through it (with my mouth more easily in one direction than the other. I guessed that there might be a tiny check-valve inside for the purpose of keeping the hoses to the nozzles filled so they can squirt without delay.

In any case, after investigating on and off for months, I found a simple plastic T-connector with the right dimensions, I installed it, and all is well.

If there is any squirt delay owing to drain-back from the nozzles, it's only a fraction of a second in duration.

I consider this a 100% fix.

UPDATE: After about 6 months, the sprayers continue to work just fine.