Burden of proof is on the manufacturer to prove that an after-market part was actually cause of an issue that occurs after the part is installed. If you owned a car, installed a hitch to only carry your bike, and your engine blows down the road, the manufacturer can't just go "Oh, you installed a hitch, so you must have been towing things that exceeded the maximum rated tow capacity of the car, so we're not replacing your engine under warranty".
Now if you installed a hitch, then posted a video on Youtube of towing a 1,500 boat with your non-tow rated car, and THEN your engine blows....that is another story.
BINGO! - WOT