Today I've changed the original spark plug (at 14150km) with an NGK C7HSA and i've start the engine ,run it for about 4 min and when I've taked it out I find oil on thread the top of the spark it wasn't wet ( but it was black I think is beacouse of airfilter ,I didn't change yet and it could run rich) or it can be from the oil ? so do you have oil on spark plug ?