I use Delo 400 for summers when doing extreme off roading and for winters I use ATF. If you consider using engine oil, make sure its a HDEO which has the necessary shear strength to cope with the gears. Regular mineral based engine oil would shear very quickly.

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99 Gurkha with OM616 IDI turbo

2015 Gurkha with OM616 DI turbo

2014 Rexton W with OM612 VGT