I lost a bit of power on the freeway yesterday, and I checked things out a little bit and found a blasted spark plug, the insulator was missing and it was black and nasty- maybe with oil. Is that cylinder shot? What would cause it to be ruined like that? They are not old, only maybe 3 months. I replaced all plugs and it still runs like crud. like the timing is off or something. Thanks if anyone has advice.