+1
The dealership cannot legally VOID your entire warranty for having aftermarket modifications. However, they can deny a warranty claim if they can prove that the aftermarket part caused the problem.
That is not true. They can void the entire warranty for any modification. It is stated quite plainly on page 11 of the warranty booklet.
They are very vague about "Alteration, modification, tampering, etc.." on Page 11 (2008) of your Warranty Information Booklet. They do not define what "Alterarion," "Modification," or "Tampering" are, nor do they use the typical "Including but not limited to" legalese, but rather a more informal "etc..." However, this does not change anything.
The argument will probably be made by someone that it is a warranty booklet and not a contract. But, if you look at the standard sales agreement that you signed when you purchased the car, it says:
"THE PRINTED NEW VEHICLE WARRANTY DELIVERED TO THE PURCHASER WITH SUCH A VEHICLE OR CHASSIS AND HEREBY MADE A PART OF HEREOF AS THOUGH FULLY SET FORTH HEREIN IS THE ONLY WARRANTY APPLICABLE TO SUCH A NEW VEHICLE OR CHASSIS AND IS EXPRESSLY IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING ANY IMPLIED WARRANTY OF OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE"
I am not a lawyer, but it seems that this language makes your Warranty Information booklet enforceable as part of the sales agreement, and you agreed by signing to follow maintenance according to the appropriate schedule outlined in the book.
In my non-legal opinion, it would seem reasonable that your act of modifying the car to increase performance would easily be considered a "modification" according to the definition on page 11, making your entire warranty void.
You might get a lawyer to argue your case (emphasis on "might"), and even if you could, it would cost you more than a new MS3, and you would probably lose. At least, if I were on the jury, I would see it that way.
Funny things about contracts. They are enforceable whether or not you read them before you signed them...