Ok, so I apologize if they look over my previous post and add it in but here it goes.
Now, before you start doing this, know that it is pretty involved and will probably take up your weekend. You will see why as you read on.
Here are the things I did and would now do with what I have learned fixing the issue.
During the whole process, getting in the car and having a friend spray the car with a hose to simulate raining is a good way to troubleshoot.
1) Before you go tearing into your car, yes replacing the rear taillight seals is the correct first step. Even if it is not the immediate problem, it will become one eventually so it is a good idea to go ahead and replace it. Careful when tightening the nuts as I actually over-torqued one of those nuts as well. Using 1/4" drive tools will help with not over-torquing. It does not leak though so that shouldn't be your issue.
2) The next thing to check is the moonroof drains. To inspect these, you need to take out all of the trunk lining to expose the sheet metal. There are four drains, two that run to the front and two that run to the back. Your moonroof will leak slowly around the seal but the water is collected and drained through the four tubes. The end of the tubes fit into fittings that lead the water out of the car. To see this, you need to look inside the metal "cage" by the wheel well. I find that it is easiest to use your phone camera to see in there. To check if this is your issue, carefully pour water into the collection areas of your sunroof on both sides, then see if water is leaking from either the connection to the pan on the roof, the connection at the rear wheel well, or the tube itself may be damaged (unlikely). To check for leaks I think the best way if to put a dry paper towel around the base of the tube and see if it comes out wet or dry. When I was trouble shooting, these were not the issue so I don't know exactly how to fix them unless it is as simple as reattaching the tube. They run through the B pillar so they are a bitch to get to if they need replacing I imagine.
**Note: The next steps will require you to remove the headliner. While you have it out, you might want to paint your headliner black like I did. Just use some fabric paint with adhesive promotor for plastic pieces and it comes out really nice There is a DIY in the huge DIY sticky**
3) If you have done the first two steps and it still leaks or just want to make sure it is sealed, go buy some silicone sealer. This is what I used:
https://www.amazon.com/2-8-Ounce-Si.../dp/B000PSB1VY/ref=sr_1_1?ie=UTF8&qid=1484610802&sr=8-1&keywords=dap+automotive but anything like it should work fine. What you need to do is seal up all the leaking areas which are:
a) Under the Rubber Roof Trim - take the trim off by pushing the back end toward the middle of the car and then lifting up. It will probably be really nasty in there so clean it out. Next check for hairline cracks in the valley of the trim seat all the way down the car. I found some in the from and the back where water would collect. Seal up any cracks.
b) At the top of the hatch opening - Right where the hatch meets the roof, there are overlapping layers of metal that could leak. Seal them up. Once you seal it though, dirt and stuff will get in the silicone. I painted over it with touch-up paint to at least make it not collect dirt. It worked, and you don't notice the sealer up there unless you are looking for it.
c) Same as b) but on the inside - On the interior, again where the metal layers meet. You may not want to seal this area up as if water gets in but can't get through, rust could occur. I went ahead and did it figuring that it would evaporate out if it ever got in but that is up to you.
d) THE REAR WASHER NOZZLE - I spent forever looking for this guy. Disconnect the feed tube and then remove it through the top **DON'T JUST PULL IT OUT!** There are tabs on the inside that need to be pushed with a flathead or something. It is a bitch but that is how to do it. Then just seal up that opening with the factory gasket that is between the roof and the nozzle. I sealed the nozzle to the gasket, let that try, then sealed the gasket to the roof. After cleaning up any that had squished out, looks like new.
**If you are wondering, leaking from this area does not make you headliner wet as the water sticks to the metal and finds its way to the trunk so even if the headliner is not wet, this could still be your issue**
e) Miscellaneous - After sealing these up, feel free to put a little anywhere there is overlapping metal just to be safe. While the headliner is out, I found a couple very minor leaks in the front as well, so be sure to patch those up while you're doing this.
4) I had rust in my trunk as a result of the water getting to I scraped away all the rust, bagged up the whole car, and painted the trunk area with bedliner or undercoating. Not only does this prevent more rust, it also keeps the interior a little more quiet.
That is about it. It takes a little while but is worth it to prevent the sloshing in the trunk! Make sure to check for obvious things such as ripped seals around the hatch and stuff like that. As for the vents being the issue, if the car was in an accident or something, then maybe, but I really don't think they would be a huge issue as not a lot of water gets to them anyway. Some people silicone around the headlights themselves. I would not advise this as it doesn't really fix the issue, looks bad, and will make taillight removal in the future suck.
I hope this helps! Good luck! :vtec: