Plenty of oil threads around, do a search, for a high mileage engine, a HDEO oil would be nice, Delo 400 or Mobil Delvac Super would clean up the internals nicely.

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99 Gurkha with OM616 IDI turbo

2015 Gurkha with OM616 DI turbo

2014 Rexton W with OM612 VGT