Yes, you should dispute it. There is nothing that indicates that all replacement parts have to be factory parts. If that was demanded by the manufacturer, they would have to supply the parts for free.
Your vehicle has a 5 year 50K mile emissions warranty. It covers all emissions components 100% for that period of time, even if you are not the original owner. The dealer is the one who "fixed" the spark plug problem. Therefore, if there was a misfire, it's their fault.
If you get no satisfaction from the dealer, look in your owner's manual for the zone rep from the manufacturer and tell him what has happened and the repair should be under warranty. Also, explaine that there was a misfire that was immediately taken care of by the dealer and no other check engine light came on to warn you of a problem.
Let me know if you have other questions.
Saturday, May 22nd, 2010 AT 11:28 PM