u/JohnCenaBoiWill

For the longest time, I've had water ingress issues with my tail lights. I tried replacing the old stock gasket with butyl tape, which should have sealed it forever, but after a month, the leak inevitably returned. So where was the leak coming from?

If you have a look above the access holes, there is a seam between two pieces of sheet metal. Upon closer inspection, the paint that would have filled the crack had split, allowing water that builds up above the tail light gasket to overflow into the car, and then into the tail light, from the inside!

So if you've got water ingress in your lights, ensure this seam is completely sealed.