The Manufacturers Love It When You Use after Market Auto Parts. It Gives Them an Excuse to Turn You Away
Usually, when you take a car in for some kind of inborn tea service, the service department of any car company will instruct the mechanics to look very closely for any aftermarket auto parts that have been used anywhere near where the failure in question has occurred.
Often, the claim processors at these companies will automatically deny any claim that comes in where they have an excuse like this. They'll do this because they know that about one out of three people just hate the idea of arguing or fighting for anything. They'll just take no for an answer.
What you have to know is that if you're caught using aftermarket auto parts, that's no reason why they should deny you your warrantee claim. Before they do that, they should be able to provide reasonable proof that the product question had anything to do with failure.
For this to happen to you'll have to get an expert witness in who will be able to credibly assert that it isn't likely the part used had anything to do with the car failing. One way you can find such an expert would be to call the manufacturer of the part in question and ask if there have been any cases where anyone's experienced failure such as what you've experienced, and ask if they are aware of any experts that make testify to that effect.
Sometimes, they will have something in their product literature that talks about what use of their parts does to original equipment warranties. At other times, if you describe the problem to them they may be able to come up with an expert technical assessment.
Often, you don't even need to really prove beyond a shadow of a doubt that you're in the right. You just need to show the dealership that you're pursuing proof vigorously enough. They just wants to see that you're someone who cannot let this go easily.
Try to collect as much documentation as youcan to show that you're not letting this go easily. Put everything you can get together into one folder that can show the dealer that you're serious, and he'll probably begin to back down. If the service manager doesn't want to be reasonable, the owner of the dealership might be the next