I have noticed I had had a fair amount of water in my trunk lately. At first I would see a little on the plastic tray that covers the battery. I checked the trunk gasket and it looks ok but I put a light coat of silicone on it anyway. Now during the last few weeks the well that houses the jack on the driver side of the car has been filled with water. I drain and dried it twice but it seems to collect more after a few days of rain or if snow is left on the car. The main floor and trunk mat is bone dry so I don't understand where the water is cominmg from. I felt under the rear window and looked with a light to see if maybe the rear window could be leaking but I don't see any stains or feel anything wet. The rear antena is in that corner be I can't believe it would let in that much water. The well just starting filling a few weeks ago and I had no water all summer long except the little bit on the battery cover in heavy rain. Any ideas?
I would try replacing the taillight gaskets. this happened to me once. I replaced everything i could think of but didn't work. Then i replaced the taillight gaskets and that fixed the problem.
Either what he said ^ Or, check to see how far your boot is popped open. My boot occasionally is a little bit open even when it's closed. It's due to the latch kind of sliding outwards a bit. If you open your boot, you'll see a latch and a nut right in the middle, where it would enter the car's chassis to lock itself when closed. Keep turning the nut counter-clockwise to tighten (yes, counter-clockwise) until you could close the boot and it lays flush against the car's chassis. It being open allows water to enter my trunk side-wells as well. Once tightened, no water should get in, assuming you don't have any rust letting water in or assuming your gaskets are good.
In addition to the tail light gaskets, consider replacing your antenna base grommet if it is the all-rubber type. You could apply some silicone on the underside of it instead, if you find it to be leaking. Recruit someone you can trust, remove the carpeting from the left side of the trunk, get in & have the friend douse the external trunk area with water. Hopefully you'll see where it's entering the car.
One more thing to check: There is a body seam about 3/4 of the way toward the rear of the car where the trunk gasket groove goes. I have seen E30s leak if this is compromized from a rear panel repair or replacement, or from simple age (it is filled with body filler and sometimes it cracks out.) After the taillight gaskets and antenna grommets, this and the trunk gasket are the biggest leak causes I have seen on E30 trunks..
Didn't realize this was such a widespread problem - I thought maybe I was all alone... I've seen reference to leaking sunroof drain tubes on the E30 causing this, but nothing stating where these drain to or where to look for the leak/disconnected line. I am having the same problem (water in the jack well) and all my seals are good (lights, trunk, antenna) - this is my last option but I don't know where to start looking for the leaking sunroof drain tube. Anyone out there know?
Pull everything from the area, dry it off, then open the sunroof and pour water down the driver's side channel (make sure that the rear of the car is downhill a little.) If you get water in that well, then you know that is where it is coming from. If you still can't figure it out, knock out the drain plug to keep water from collecting.
