The leak is less likely to be coming from the taillight, it is more likely coming in around the panel that has the spoiler motor under it, the joint between the gas filler cap and the fender or one or both of a broken or loose corrugated hose at the top of the tailgate where the wires for the license plate light and air line goes. On an SRT it can come through the same gasket around the spoiler mounting plate or the joint between the spoiler supports and the plate. Look for rust around the license plates lights. Also a poorly fitting seal around the hatch or trunk lid could be the culprit.
What car do you have?