Most likely it was not sealed well when installed. Depending what sealer was used you may be able to clean it and re-use it. Possible the gasket is damaged. Who installed it? Was there any metal repaired or possibly should have been and wasn't? I did my own and helped Hoppy with his. They aren't that hard to do, but can be tough to get positioned right in the seal. They are completely different than a modern widow install, so many guys that could do a great job on a new car don't have a clue what to do with these.