Rain water leak to inside cabin

[XP900]

I have the well known water issue in the passenger side ...usually always collects in the back floorboard. My two cowling drains are clean and flow water well. I had it parked on a hill facing upwards during the last rain storm so that is when it took on water. 2010 Model Year. Read a lot of Mustang forums but usually earlier or later model years and there are some differences.
Anyone have this issue and find out where their issue was? I dread ripping apart the inside trying to find this but may start with just carpet pulling to see where it is actually coming from...front or back

 

[XP900]

I have the well known water issue in the passenger side ...usually always collects in the back floorboard. My two cowling drains are clean and flow water well. I had it parked on a hill facing upwards during the last rain storm so that is when it took on water. 2010 Model Year. Read a lot of Mustang forums but usually earlier or later model years and there are some differences.
Anyone have this issue and find out where their issue was? I dread ripping about the inside trying to find this but may start with just carpet pulling to see where it is actually coming from...front or back

Spend last two days on an off pulling up the carpet and inspecting the engine and fender bays. My cowling areas were completely clean and the rubber duckies worked as they were supposed to ...still pulled and cleaned anyway. Used urethane to seal the seams in the cowling top and around the hood hinge area even though I saw no breaks in the original urethane and had no gaps in the firewall holes for the engine wiring and door wires. Used a hose and sprayed the outside areas of the cowling, car and door multiple times using hose pressure and sprayed into every crack and seam I could find. No leaks at all inside anywhere on the passenger side. Finally gave up looking for a leak (even checked at A pillar area) and started putting everything back in.

I realized something too. I have only noticed water in the back passenger only a few times and it is random (no mold anywhere and relativity clean under the carpet after dried out). When this happened this time I had the car parked on my driveway facing up hill and it is about a 30 degree slope. It rained heavy the night before I noticed the water in the back pass footwell . I think the rubber boots in the cowling may not be quite able to keep up with the water flow and since the car is angled so much it may be allowing the water level to just reach the bottom of the cabin filter and leak in (front carpet was wet and water naturally settles in back seat footwells on level ground. I am no longer going to park my car on the slope and wait and see if the problem is resolved. Based on how much water was in the back seat I think I should have found a seam dripping using the hose if there was one. Pulling the boot may be an option too.