Rear Suspension problems of the 1999 Nissan Quest

After vehicle reaches 17,00 miles steering wheel and front began to shake giving the vehicle a rough ride. The vehicle was taken to the dealer and was diagnosed as having bent rear axle. The vehicle was never been in accident so the bent axle should be manufacturer defect. The tires are worn prematurely, but the dealer refused to pay for the replacements claiming at 17000 miles it is a normal wear.