I too, have a leak in my trunk. It only happens with heavy rains, and I don't have a sunroof. I got in the car, and had a friend take the hose, and spray all around the deck lid. I found it to be the seal around the deck lid to be the culprit. It only seems to happen when a lot of rain passes around it, before it can drain, since the seal sucks. A complete replacement of all weatherstripping for my car, is available through JCW, but for $80! Guess I will have to wait to fix it.
'89 SSE - GX3 -190k, 155k on body - Back for another ride.