I will add to this discussion about your dealership stating that your warranty is now void. Get that in writing by the service manager RIGHT NOW! Take that letter and send it to K&N IMMEDIATELY!
See what this says right here?
The use of a K&N air filter will NOT VOID YOUR VEHICLE'S WARRANTY! So, if your dealership believes they can void it, you can sue K&N directly for lots 'o money. They will, in-turn, sue your dealership for lots 'o money!
I get really irritated with overzealous service centers stating silly things like this. THEY have to prove that your vehicle was damaged by an aftermarket part, and if they can do that, then K&N is on the hook for all repairs after that, simply because they stated it in their documentation. Sadly, dealerships like to play god and hold shit like this over their customers to make them feel superior. While I won't say good or bad things about K&N filters, the facts here are that you have lots of rights as a consumer against this type of stupidity, and the quicker you put the dealership on notice, the sooner they'll know not to play stupid games with you. Of course, do this without being an ass about it, but let them know that if they aren't willing to put it in writing right now, then they need to stop making ignorant claims.