Thank you so much. That helps a lot.
I held a towel directly behind the roof gutter to isolate it, poured water on it, making sure it didn't drip down to the seams, and water still got in. So I'm 99% positive it is under, or directly behind the rubber trim over the rain gutter.
I actually did a serious deep cleaning to my car after I bought it off craigslist. Took out ALL the interior, save for the dash. Carpet, all the seats, plastic pieces (around the hatch door too), headlining, looked like a rally car in there. Figured I'd find all the leaks while I could see them easily. It had leaks behind both tail lights, a leak coming through a separation in the sheet metal seam around the gas cap door, and through tiny cracks in the hatch door at the corners which you can see the black silicone on that picture. Each time I sealed one and tested with a hose, the amount lessened.