Water continues to flow out of the mixing station when the water inlet ball valves are in the closed position.
One or more valves are no longer forming a complete seal. This can be caused by physical debris from the water supply, worn internal components, or damage from freezing.
First, try tightening the handle on the front of the unit with a screwdriver. If still leaking, the valve will need to be removed for inspection and likely replacement.
To confirm which valve is leaking, remove the discharge tubes and observe which injector body continues flowing (slightly) when the ball valves are all closed. Details below.