Use this guide only as a last resort: [Wayback/Archive] BMW E61 Trunk Leak – Sunroof Drain Failure – 2004-2010 5 Series Wagon.
Try first to remove any debris from the drains from the panoramic sunroof/moonroof side or remove the valve with grommet at the lowest end. Some YouTube video’s explain how to do that.
It looks like a sunroof often has front drain holes clogged and a panoramaroof often the back drain holes; where it leaks depends how your car is tilted while parked.
You might want to move the electronics that are in the well under the spare wheel to the left hand side of the trunk.
Furthermore, the electric cabling on the E61 that runs underneath the hinges of the trunk and trunk window mechanisms tend to break over time causing all kinds of electrical issues.
A list related to those first:






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