Water Leak In Rear Cargo Area

My leak was from the gas cap area.
I found it by hosing down different areas of the car.

I still have a small leak from somewhere I can't find. But after sealing that up I get much less water in.
I thought mine was from the LH qtr window as stated by previous owner but when I checked it out myself, I noticed the water sheeting down into the filler area. sure enough that's it. How did you go about sealing that one up so I can get a game plan?
 
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02 Protege LX, 03 P5 (x2), 09 Miata, 07 Mazda3, 13 Fit, 09 Ody
I thought mine was from the LH qtr window as stated by previous owner but when I checked it out myself, I noticed the water sheeting down into the filler area. sure enough that's it. How did you go about sealing that one up so I can get a game plan?
Just bought some silicone sealant and slathered it around the edges.

There is also a gasket behind the filler. I did not replace it. Probably a dealer part. Or you could get some gasket maker.