i haven't gone through that personally, but i know how dealerships are with not wanting to do the work they are supposed to do. If they are giving you shit about it tell them to put some OEM spark plugs in and see if the problem is still there. Just logically explain it to them and make them feel stupid for thinking it's a spark plug problem.
EXTERIOR MODS: ...basically just a lot of paint and skulls... and painted skulls.
Official Mayo Hater #3