So I'm vascilating on which fix mentioned is the first one to try. The drip is very steady ... when it's leaking! We had it dripping steadily on July 4th after filling water bottles for our road trip. It was so constant that I didn't feel I could leave a reservoir on the floor as I was afraid it would overflow while we were away. I turned off the supply valve, placed a resevoir on the floor and left. When we returned 12 hours later the resevoir was full and over flowing! I emptied it and cleaned up the floor. I put a water glass under the dispenser and drained the rest of the line. (There wasn't much left).
That night it was of course fine. I turned on the supply valve the next morning and pulled some glasses of water. Ice maker resumed operations. And since then, of course, no dripping or leaking. It's all fixed! Until.... the next time it starts leaking.. which may be later today.. or next week.. or next month...
So... is the John Guest valve cheaper and therefore the right first try?
And BTW- I appreciated everyone replying with ideas. Thank you for taking the time.