I just bought a Mazdaspeed 6 with 73K on it. I am changing all the gearbox oils to Redline tomorrow (MT90 trans and 75-90 in the transfer case and rear diff), and I need to change the engine oil too. I was thinking of using either the German Castrol or Mobil 1 synthetic 0-30 in the motor. any suggestions? I hear there are issues with excessive amounts of fuel contamination after the oil has been in there for a couple thousand miles. I drive 35 miles each way to work, and I get about 75% of it in traffic. On weekends I drive 25 miles to see my girlfriend in Los Angeles and drive around on LA streets during the day. Southern California has pretty mild weather as I am sure you know. I am going to use the Factory oil filter and I am looking to get 5K between oil changes so i am not doing a change once a month. The car is stock except for a AEM cold air. What does everyone think?