Looks like a corrosion problem? What's your model year? The Nissan corrosion warranty is 60 months, unlimited miles, at least for my 2014.
I would escalate the issue to Nissan USA. Send them the photos. They should help with the reluctant dealer, if you are still within the warranty period.
Good luck.
I would escalate the issue to Nissan USA. Send them the photos. They should help with the reluctant dealer, if you are still within the warranty period.
Good luck.