Last night I submerged my lights and I had one side leak. So I went over it with a pen light to see if I could find any type of spot where it could possibly leak and found a few pinhole leaks.
I then removed all of the silicon that I had put on the tabs because with the sealant they put on the lights, when you reseal them, there may be small leaks on the side that you can't see. So I took a knife and cut down all the gray sealant they put on the lights so it was flush with the black housing. I then reapplied the silicon with a Q-tip (with the cotton removed). Went over everything with the pen light, and when I figured that everything was ok, submerged them again and they didn't leak.
So…this is what I did and/or recommend.
First look at the tabs on your lights. Cut down any sealant so that you can apply silicon and see the entire tab hole, not just the front and the sides. Apply 2 coats of silicon. First just fill the hole and use your finger to push it into the hole farther. Once that is done and dried get a flashlight and inspect every tab. Make sure that there are no pin holes in the silicon. I think this is where everyone gets frustrated, because pinholes are so hard to find. If there are, apply silicon with a Q-tip and smear the silicon over the entire hole again. You may want to do all the tabs again to insure that they're sealed.
Second, apply silicon around the taillight where the clear housing and the black housing meet (the part that would face the car behind you). Do the same thing as you did with the tabs. This will take a lot more silicon to do the edging, especially on the top. Then use your finger to push it farther into the crack. The more smooth you are with applying the silicon the better the lights will look because you will be able to see the silicon bead through the clear plastic. Any excess I used rubbing alcohol and a cotton ball to pick up. You'll use quite a few cotton balls. Once that is dry check for any type of holes again. I had found 1 or 2, but I went and applied another coat of silicon over the whole thing just in case I missed anything.
Once you've gotten this far, be sure to check the fixtures again for any type of holes. I had submerged my lights as far as I could under water without getting water coming into the holes for the bulbs and I didn't have any leaks at all. I will probably wait a week or so and apply another coat just to be safe.
I don't know if this will help anyone else with the Altezza problem, and I can't be sure that mine won't leak. But with what I did to reseal them and submerge them, I was able to stop mine from leaking.
