I would sue them (at least in Small Claims court). And also make this viral. Don't underestimate the power of social media...
This is not a defect warranty issue. It's a substandard material issue! Imagine your chassis starts buckling because of metal fatigue, and it is caused by inferior material. Or welding. Even if the 5 years is over, Mazda cannot be allowed to just wash their hands with "warranty over".