Nissan Navara ST-R 2010: Faulty defogger

The rear window in my 2010 Nissan Navara ST-R suddenly cracked when I turned on the defogger. I tried to claim it under warranty, but the dealer told me it's hard to prove if it was due to outside elements or because the defogger was faulty. I ended up paying for the repair myself, but can I still ask Nissan to repay the cost of the job?