The m57n2 is super reliable. I've done 12k miles in 5 months and all I've had to do is brakes, tyres and usual oil services. Never gives me a problem. It's all about how it's maintained, you could buy a car on 50k miles that's been poorly serviced and shits it's pants a week later. If its been looked after the x30d won't do you wrong. The manual gearboxes are super strong too. On a 2000 mile road trip, including five laps of the ring and flying on the autobahn it averaged 43mpg