All I have to offer is I found a pin hole in the plastic water line. I cut that section out and with in a day another hole in the old section of line.
You might have a more complicated problem than I had. If you want to turn off the water to the ice maker there is a small brass in line valve behind the panel where you attach you water fill hose.
The panel is held in place by velcro. So simply but gently pull the panel off and you will find the brass valve.
I have not run a new line yet. I don't drink the water from our fresh tank anyway. I buy ice.
Hope you find your issue.
By the way, plastic has a memory, and it's usually a bad one.
Plastic parts last 10 to 12 years and then they are dried and brittle.