If the leakers are on the top row, it is the seal between the colored plastic lens and the tail light body. The water runoff from the top and down the rear window goes into the seam between the fender and the trunk lid and runs right down that channel and splats into the upper three lenses right at their seal point.

You might avoid drilling the usual drain holes by sealing up the lenses. Only the clear reverse light is supposed to come off. If the others come off, well - there's your problem. If the others don't, forcing them will likely break them.

With the tail light off the car, clean the sealing area as best you can, and run a bead of good marine silicone seal between the body and the edge of the lens. If time allows, do it in two passes to be sure you get a good seal. It shouldn't be necessary to seal all around the far end of the outer lenses.

In my pre-BBRD days, I was disgusted after find that, having the same problem as you, removing the tail light and gasket, and sealing the gasket to the tail light and to the car body, and still getting leaks into the trunk.

Good Luck,

Bob

:>)