What has basically happened here is calcium has built up inside the fill valve causing the valve not to shut fully, this is allowing water to seep into the water system causing your problem. Unfortunately Delores the valve is not serviceable so it will need to be replaced.
To do this pull the unit away from the wall and take the lower panel out at the rear. You will see the valve behind this panel. At this point it will just be a question of a screw and swapping water lines and wires from old to new valve.
Below I have included a link where you can purchase the replacement part :)
To order your replacement part >>>>> CLICK HERE <<<<< To order your replacement part.
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