Christian, Many plastic coolant bottle failures are at the bottom seam and cannot be detected unless the leak is in progress. To determine exactly where the leak is originating conduct a cooling system pressure test. If you don't have a pressure tester most service facilities do and can perform the test for you. "We're here to help you" DMC Help / De Lorean Services / <dmchelp@xxxx> Web Site: <www.deloreanservices.com>