The leak in the trunk is a common problem with all/most 3 series. I owned an 87 325, sold it and now have a 90 325ic. Both had the same problem, which stemmed from the seal around the left tail-light getting old and worn out. Take the lens out, and go around it with some silicon and seal it back up. This cured my problem in both vehicles. Good luck and let me know if it works for you.