So I've gotten it down to one drop every, on average, 57 seconds. Basically, my hypothesis was right: I did poorly the first time taking my time with the patches and there was too much room under them for water to keep getting through. I've discovered that the vinyl patches with the brush-on epoxy are no bueno for me. It might be because the area I'm patching is just too big that the adhesive is not staying uniform under the patch, especially once it goes underwater. The self-sticking patches have proven significantly more effective.
I believe I'm at my final roadblock. I did the dye test to see where the water is coming from still, and unsurprisingly, it's along the seam. A very, very slow trickle is getting under the patch right where the seam is, through a gap I would estimate at no more than half a millimetre (if you know your metric). I tried endlessly to get the patch flush against the seam but I think the gap is just too small. Does anyone have any suggestions? I've seen some YouTube videos of folks using stuff like WaterWeld (the waterproof putty), anyone think that might work? Is there anything else that is viscous or malleable that would work underwater that I can apply along the top and bottom of my patch where the seam is and the miniscule amount of water is sneaking through?