could be the antenna, roof seam, or the rear draintubeIts seems it leaks in the driverside rear of the cab. It drips off the headliner onto the back seat and fills the area under the seats.
Most of the time we dont see the actual leak. We just notice moisture in the cab of the truck.
We have been taking it to the dealer when it looks like rain clouds are forming in the truck since its closed up tight.
All the moisture really had done a number to the appearance of the interior!