I mean, I have an aftermarket stero in my car and I went to the dealer to get the blindspot sensors replaced. They honored the warrenty and replaced the sensors

I mean, I have an aftermarket stero in my car and I went to the dealer to get the blindspot sensors replaced. They honored the warrenty and replaced the sensors at no cost to me. In your scenario, that's also exactly what small claims court is for, or also contacting the manufacturer directly. In another scenario, a ground wire went faulty and a (shadier) dealer tried to get me to pay for the cost of the diagnostic. I said I can chat with GM about that cost and they very quickly said they would waive the fee.