Brought my car in for an oil change and supplied them with 8 liters of oil. The tech put it all in! I went to check it and it was a 1/8th of an inch above the full level on the dip stick. This was after I went on a road trip. The car did sound kinda funny when I was pushing it above 160km/hr...like a low droaning sound. I brought it back to the stealer and they said that 1 liter extra won't hurt the car and refused to drain it. Is this true? I heard it kills your spark plugs... What else could go wrong or are they telling me the truth???