Wet again

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Try this:

Pull out all your floor mats, lay down multiple towels (especially around your DME) grab a small flashlight and go find a touchless carwash where you can sit inside and witness the problem firsthand. Not a lot of water volume there but enough to give you a good idea where the problem is. This should show you where to look. Preferable to laying yourself down at the mercy of the stealership.