"Damaged Driveshaft?'

[Heff]

Hello everyone, I've been on the forums for quit awhile now browsing but this is my first post. so to start off my story/question I have a '16 370z base model with a six speed and 5900 miles on it I've had it since February. The only mods I've done so far are a Invidia CBE, Berk HFC and a TWM short throw shifter. A few weeks ago I started to notice a buzzing/vibration coming from what sounded like the inside towards the hatch on the passenger side but couldn't pin point it. So I decided to take it into the dealership today to get it checked out and ended up with them telling me that the dust boot from the shifter had come loose and melted onto the driveshaft causing damage to it and that it needs to be replaced along with the boot and its going to cost me 1300 with labor and parts. So my question is, would that be something that should be covered under warranty, should I go get another opinion on it? Are they just trying to get money out of me or what? any help is much appreciated and if anyone knows of any good shops they'd recommend, I'm in the phoenix, AZ area. Thanks again