Ok, I have found that the source of my trunk leak is this vent thingamajigger on the left side of the trunk in my '91. It leaks from around the perimeter of it. My question is how do I get to it to seal it? Am I right to assume I have to remove the bumper to get access to it?

 

Is it leaking into the trunk from there? Or is the antenna, going on memory that is the side it is on, leaking and looks like, puddling around that area. The outside area of the vent, isn't a place where I think water would "come into" the trunk....trust me I really hate water leaks. have you used "baby powder" or some other method of confirming that is the source. If that is the source, why remove it, just seal the inside part. If it had a sun/moon roof then I would offer another suggestion.

 

Yeah, I had the garden hose running on the fender above the bumper "seam" and below the antenna and it leaked in around the edges of the vent. The thing looks like it was pushed in from the outside on the assembly line. Maybe there is a small flange on the outside, hidden from view when looking at it from the trunk? Thought that to seal it best, I should remove the vent and caulk it from the outside...

 

Air outlet (#26) installs from the outside. There's probably a gasket kinda like the tail-lamp assemblies have gaskets. Taillamp gaskets leak too...

Since it sticks into the trunk space, you probably CAN caulk it from inside the trunk. Not sure how much pain it involved in removing the bumper.

 

I had a water leak on both sides of my 90 accord EX.
Turns out it was leaking at the taillight gaskets. The black gaskets pull away from the body and create a gap and an opening for water to enter the trunk.
The water runs down the trunk channel and directly into this gap.
I can see that there is a gap present in your photo.
Verify the leak with a hose and direct the water down around the trunklid/ body opening, then open the trunk and you should see water coming in through the tail light area.

Here's how I fixed my leak:
Clean the gap area with Isopropal alcohol and an old toothbrush.
Apply a thick bead of Black Silicone (flexible) caulking to close the gap.

 

Not leaking from taillight lenses...I have replaced all four and tested...it does leak from the vent.

 

I have a sunroof on my '91 SE, and it has a leak in the trunk. I know it will leak because I put a towel down, and the towel is always damp. There is condensation on the trunk lid. The water leakage fortunately hasn't damaged any personal belongings, but the condensation has corroded the ABS computer in the trunk, so my ABS light is always on. I think my trunk leaks in multiple places, but I am unsure as to find out where they are. Living in Oregon, we get a quite a bit of rain, so you can see how this is a little bit of a problem without a garage. What is your suggestion for a leaky trunk when there is a sunroof on the vehicle?

 

The sunroof has drain tubes from each corner, you can check the ones for the rear corners. They should go down to the trunk low & way outboard. Probably have to remove all the carpet stuff from the sides of the trunk so you can see the fenders & the antenna motor. Look down there somewhere for the hoses. They plug into some kind of fittings (#7 & #8) but maybe they've popped out?

 

Normal places- but add the sunroof drains. Where exactly in the trunk is the water coming from or standing.

On the 3rd gen's there is a "tube" that gets clogged. From under the car, look up inside the bumper, on the outside just behind the rear tire (rear qtr panel). You should see a small little rubber "vent thing"-sorry don't know what else to call it- if you insert something soft- plastic zip tie, weed eater line, ect- into that tube and clean it - be carefull because if it is clooged there is a good chance water is going to come out. There are four in total-two front-two rear. If anyone ever wants to know about the front drains-send me a PM.

EDIT: too slow at typing again...Jim has pic's so I like his better.

 

It collects in the back left corner of the trunk (back being closest towards the rear of the car) I have school this week, but this weekend I'll pull all of the carpet out and figure out where it's coming from. Thanks for the diagram and the tips- I'll reply back with my findings.