I've checked the iDrive and dipstick on my car when collecting it from a dealer service and found the level to be on minimum.
Then walked into the Service Dept and been given a 1L bottle of oil to top it up.
Apparently they "always use the specified amount of oil". I call BS on that
Yours could have also been under-filled.
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Current : F31 330sD, remapped, Ohlins Road & Track, Millway camber plates, Quaife LSD, Stoptech brakes + Pagid RSL1 pads all round, Weichers front strut brace, Eibach front & rear anti-roll bars, Michelin MP4S.