I just pulled out my factory plugs and they were nasty looking they were all corroded on the outside. I'm only at 55k and my car is a 09, something tells me those factory plugs were dirt compared to the iridium ones to begin with. The ones I pulled out were ac delco but the one of the numbers were different than my ac delco iridium plugs. If they last so long I don't think they would be corroded. Not to mention the bolt that tightens the spark plug was crap too I ended up breaking one by tightening it, just decided to buy 4 new bolts that were probably alot better than the factory stuff. My car wasn't running that good to begin with but after changing the spark plugs and the oil to pennzoil ultra, putting in some zmax and fuel cleaner its not running a ton better.