Today I checked the oil level with the dipstick (I hadnt done this for a while) and the level was below the low level marking! I didnt get any of the warning lights as described in the manual, is it possible that I damaged the engine?
Also is it normal that the oil is so low after 12,000 km? What kind of oil should I be using for a diesel engine?

Thanks for the help!

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August 2011 X5 3.0d