DIAGNOSIS The membrane touchpad is wearing out or has a layer of grease/film disrupting the electrical contact. Spills are a common cause.
FIX Unplug the unit. Clean the entire keypad area thoroughly with a cloth dampened with isopropyl alcohol (rubbing alcohol). Dry completely. This removes conductive film from spills.
IF THAT DIDN'T WORK The membrane itself is failing. This is a common wear item. The entire touchpad panel needs replacement. For the EM131A5C, this is a single assembly that includes the plastic bezel and the membrane circuitry behind it.
HEADS UP Do not use harsh cleaners or excessive water. Liquid can seep behind the panel and damage the control board connections, making the problem worse.