A Condor Boeing 767-300, registration D-ABUZ performing flight DE-2114 from Frankfurt/Main (Germany) to Cancun (Mexico) with 182 passengers and 10 crew, was enroute at FL360 about 130 northeast of St. Louis,MO (USA) when the crew reported a possible fuel leak and decided to divert to Saint Louis. The aircraft landed safely on runway 30L about 30 minutes later. The crew queried emergency services whether they could see any leak from the left wing. The attending emergency services reported a leak near the left main gear. The airline reported problems with a fuel tank prompted the diversion to St. Louis. A replacement aircraft has been dispatched to St. Louis and is estimated to reach Cancun with a delay of 30 hours. The passengers were taken to hotels. A replacement Boeing 767-300 registration D-ABUP is currently enroute from Frankfurt to Saint Louis and is estimated to reach St. Louis about 27 hours after landing of D-ABUZ.