Congrats! 300k is awesome milestone to achieve. I too believe that driving longer distances every day keeps problems away. In almost all of my cars, the problems have started when they were not being used a lot. Every car that I have driven a lot has had less problems in its life time.

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Currently driving: 2011 E70 x35i , 2011 E90 335d
Previous BMWs: 2007 E90 328i , 2005 E53 3.0i, 2011 F10 535i (6spd manual)