Thank you both for the suggestions. We will give the drains a good looking over, and cleaning out. Many thanks!
To answer the question about where the water shows up, the car is parked on a slight incline, nose up, and the water was draining out of the rear seat belt shoulder harness "accessory port" (there is only one of them, on the ceiling, in the rear seat, passenger side.) It dripped on to the rubber mat (fortunately) that covers the floor of the cargo compartment.
Thanks again,
ken