Wiper problems of the 2013 GMC Acadia

Tl the contact owns a 2013 GMC Acadia. While driving with the windshield wipers activated, the wipers stopped working when the turn signals were engaged. The dealer (moore GMC truck, 84 high st, danvers, MA 01923, (978) 774-0040) stated that the contact would have to pay for replacing the wiper motor since the warranty had expired. The contact claimed to have noticed the failure before the warranty expired. The dealer referred the contact to the manufacturer who offered a $100 credit toward the repair cost. The vehicle was not diagnosed. The failure mileage was 25,000.