SeanR

I keep getting water in the back seat passenger side after rain. I took off the passenger side cowl and cleaned the drain and gasket, Still getting water in back seat floor.

Derf00

Water under the rear seat on the passenger side or on the floor of the rear seat area (where the feet go)? If it's rain water, it should leave a dirt trail from where it's coming from. If you can't spot it, the next best thing is to remove the interior panel on the passenger side in the rear and the lower back cushion itself itself and start spraying around the inner wheel wells and under the car to see if you can find where water is coming in from.

My guess would be the rear quarter panel glass on the passenger side so spray around there too..

08'MustangDude

It's usually a bad seal on that side rear quarter window.