I had flooding and ultimately it dissolved much of the wiring below the passenger seat, causing major electrical problems.
Morristown BMW originally diagnosed it as doorside vapor barrier, which they fixed for a hefty price.
I was parking my car outside constantly, so more flooding occured. Morristown BMW suggested I replace vapor barrier on other door and other electrical repair (quoted $2,500)
Denson automotive replaced the door side vapor barrier, eventually diagnosed the sunroof draining problem, replaced some wires below the passenger seat, and tuned up the car for $1,300.
Bottom line, flooding in the 530i is relatively common Morristown BMW (probably other dealers) will charge you and arm and a leg to replace items in your car, but don't have the ability to diagnose problems.
Many times, the problem is just a drain that you can fix yourself.