A few facts: - The 350 has only 6 plugs as opposed to 12 in the 320. - Once the air filter is removed (snaps out in 1 minute), all 6 coils are easily accessible, and sit right in top of the plugs. All you need to do is remove 2 tork screws holding each coil, then pull the coil out, and then change the spark plug. Your Mercedes. W203 C200 Kompressor Elegance SE 2006 Tanzanite Blue with cream interior. Mar 7, 2017. #1. Hi All. My Haynes manual says I should change my spark plugs every 4 years or 55-65 000miles. The 4 years is up, but I have 45 000 m to go. The car is running lovely. My question is should I change them now, which is my first thought, or.