But most common out of these is the failure of foam gaskets on back of the tail lamps. These are the foamy stuff between the taillights and the body. Over the years, these become almost powderized and can no longer dispel water. What happens is the rain from the tailgate gutter runs down the sides and end up around the top of the taillights. And if the gasket (the foamy stuff) is bad, the water just flows right into the trunk through the taillight opening.
(to test, open your trunk, pour some water on top of the taillamps right on the gap between the body and the taillamp)

Last time I checked, Honda stopped making these gaskets. If you can find one oem or aftermarket, that’s great. If you can’t find one, you have to make them on your own. That’s what I did. I just went to the Home Depot and got some pipe insulation foams. Get the more denser one for more protection against leaks. Also, get the largest circumference you can get to make sure they are wide enough for the taillights’ back. Also, make sure they are thick enough for a gasket.

Just make sure when you remove the old ones, try not to damage or tear them apart because you’re going to use them as a template. Trace the shape and location of the holes on a thick cardboard and cut out a template. Use it to cut out identical shapes from the pipe insulation. It will be kinda tricky because pipe insulation is all curled up from being round. But once they are pressed between the taillight and the body, they work like a charm.
This trick worked for me for 2 years and counting. Good luck.

I removed the interior panel that covers the top of the wheel well, the part that comes up to a point. On the same side, I remove the rear access panel -the ones that have no screws holding them in place. With these two panels open, I reach back between the back end of the wheel well and the tail lights. I felt a hose that just plugged into a port. No lock or anything to unscrew. Just a big clear tube into a larger diameter port.

I made sure that the tube was plugged into it’s port and then wrapped tape around the top of the port also in contact with the tube to keep them in place.

Is this the correct place to tape? If it is, are there other common places for water ingress into the trunk space of a CRX? [Honda Civic CRX Si 1986]

Now, on the inside of the trunk, the tube connection is right where your finger is pointing. If you have small and nimble hands, you can probably get to it through tail light service opening. But most likely you’ll have to remove the trim panels both rear and side inside the trunk.