How about the drain tube(s) for the air ducts? The AC evaporator condenses lots of moisture out of the air, there's a drain tube for that. I don't know exactly what it looks like on an MDX, but there might also be another drain tube to handle rainwater from the air ducts. Sometimes those tubes are just under the dash where your feet can push & disconnect the hose.

There's also drain tubes for the sunroof. Find where they're supposed to be connected at the bottom, see if they're OK.