You have to put pressure to the system and look around to where it is leaking. I had a problem with my 300D and found that when the system got hot and pressure build up, it would leak from the bottom hole in the water pump and when I would look for were it was coming from it wound look like it was coming from the bottom of the engine. I had to buy a pump that would add pressure to the system and that was how I found it. Prblem fixed.
Rob