Mercedes Benz Canada denying culpability for manufacturing defect Internet

What should i do?

 As the second owner, I have had the pleasure over several years, driving my current CL55 AMG which I maintain in near showroom condition.

Recently I noticed cracks in identical locations on the top of both front fenders; peculiarly, both cracks run perpendicular to the fender; that is from engine to tire. Each crack is adjacent to and emanates from an assembly (also cracked) under the hood that bolts the fender to the frame.  

I met with the general manager of the MB Collision repair Centre to discuss the cause and best approach to remedy the situation.  After inspection, he surmised that the damage was due to a structural flaw (assembly/stress) and not a sudden impact.

Later, he phoned to tell me that Mercedes Benz would repair the car for $4,265, but astoundingly, that I was responsible for the entire amount! That is, that notwithstanding the agreed cause of the damage, Mercedes Benz has now profited fully from the
 situation. This rationale was based on two aspects; one, I am the second owner; and two, that not all servicing was done by Mercedes Benz Canada. Neither consideration addresses the damage nor how it was caused.

Respectfully, any suggestions  that may result in a  more equitable resolution will be genuinely appreciated.