Another place for water to enter can be the antenna mounting, although that's pretty rare. Your case seams to definitely be the tailights, but you never know if another leak is contributing. A leak there could just run down the inside of the outer fender, or it could run along the antenna cable and into the trunk. (Murphy's Law will give a hint as to what path the water will choose.)
Make sure that the chrome antenna nut hasn't worked loose (or whatever type mounting nut is used if your antenna is not OEM). I would NOT use silicon rubber there, but I would use a heavy glob of silicon grease on the rubber seal then reseat it, and wipe off the excess.