Installing a new dual water assembly valve was the fix. The video on the website was very helpful. Anyone with moderate fix it skills can perform this repair, but, there might be some unexpected issues:
1. If your incoming waterline is one of those "pinch valve" external water pipe valves, you might find that shutting it off and turning it back on renders it inoperable. I found this to be the case, and ended up cutting a section out of the water supply pipe and installing a "Shark Bite" 3 way connector and an auxiliary 1/2" shutoff valve.
2. You might find that the incoming 1/4" tubing has accumulated corrosion and needs to be "blown out" with compressed air, or simply replaced.
Those 2 issues were encountered, but, all issues were remedied and the install went smoothly after that.