LG Dishwasher Model LDF6920ST: The control button for the "Normal" cycle has gradually been failing. It would take multiple attempts to get it to respond and start the dishwasher cycle. Now, depressing the button does nothing at all. The rest of the control buttons still work, and we can use the dishwasher by depressing the Power Scrub control button. Is it the button itself that is defective, or is it the control unit under the button? And if it is the control board under the button, this part does not seem to be stocked anymore, per the sites I have searched. The DW is 10 years old. Suggestions?