make your freind notice the gear select indicator on the dash when its cold - I have seen one E320 doing that and I had to change the little white selector switch in the shifter box to remedy this.

I found that when the shifter position was being seen intermittent.

This is also sometimes thrown by a weak battery

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)