Try a different dealer. I would say in your case try the dealer that uses the company who installed your aftermarket pieces. Like the above poster stated they cannot void your warranty until the problem in question is proven to have been caused directly by installation or work done aftermarket that diminished the integrity of bmws engineering. Im sure a different dealer will service the car no problem.
Worst case scenario somehow it is due to the aftermarket installation. Which I feel is highly unlikely but I have seen crazier things. I think its best to deal with the situation at the dealer who does business with the aftermarket shop. Just my 2 cents
Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius and a lot of courage to move in the opposite direction. - Albert Einstein
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