Oh wow!!! A NAISSO linky??? Damn...haven't seen those in a while.
Was a lifetime member of that organization until someone stole my ImpalaSS.
The Magnusson Moss Act is still a bit vague about who is liable for repairs under warranty when the vehicle has been modified. Obviously, a body rust through failure cannot be disclaimed because the owner installed an aftermarket stereo.
But that kind of divergence is not normally the issue.
The case that Randy describes above would be more typical where one engine assembly is modified and another one fails.
The Act provides for a process to file, negotiate or even arbitrate a dispute between the OEM and the purchaser.
Truly, you do not have to take the dealer's position on a failure being attributed to a modification as the final word if you wish to protest.
My experience has been that a long term, working relationship with your dealer and the service advisors goes a long way to reaching agreement on repairs, costs and warranty issues.
I'm kind of going through that right now. I am a repeat customer at this dealership (3 vehicles purchased there) and I have developed the relationship with two of the service advisors and the service manager. They take good care of me and I'm grateful.
I even bribe them...
On hot summer afternoons, I'll take a cooler full of ice cold Snapples to the crew. If I am dropping off a vehicle in the morning, I will stop at a local bakery and get a couple dozen mixed donuts/bearclaws/maplebars and drop them off. First of all, they seem to like the goodies and I truly do appreciate what they do for me as a customer.
So a little relationship building and goodwill goes a long way.
I'm pretty sure Randy isn't opposed to donuts...