Suggest starting with sunroof drains, easy to do and don't have to tear anything apart. Sometimes you can blow them out with just canned air or water pressure then wait until it rains and go from there. If air conditioning is the cause you should be able to replicate those circumstances without it raining.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas