I've had both 3-way heater pads replaced on both front seats on my 11 MDX Adv about a year apart. They were turning off intermittently from 1-5 minutes. Both pad replacements were covered by the warranty. It took almost a week the first time because they had a hard time getting a local upholstery person to put the seat back together. I didn't mind because they gave me a 16 MDX sh-awd tech during that time.
You might check into maybe removing the seat yourself and taking the seat to an upholstery shop to replace the heating element to save the labor cost.