Why don't you take it apart and just install the fan motor on the old housing? To be honest it sounds a bit strange that there are two separate electric fans. A viscous and electric fan is understandable but all the newer models only have one electric fan and it's enough.

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E39 530dA -02 M-Sport Messing metallic
E53 X5 3.0dA -06 Sport Stratus grey
E70 X5 40d -12 M-Sport Space grey