That hole is a water drain hole. Mine has an insert and has a small tube on the bottom of the insert. There is also a dam that is behind the hinge area from the side to the center section on each side to keep water from going further into the trunk. Also the hinge for the top has a small stainless tab that holds a small rubber gasket. The gasket is on the front of the hinge and acts as a seal when the top is up and the lid is closed. It's suppose to help keep water out of the compartment at the top hinge where it meets the body. I would show pics, but my Darrin is put away for the winter. It's up in the air on the lift, and covered. Best way to keep varmints out. That insert is actually brass, and had a small tube on the bottom. I do not know the start point of when the dam was included, but it looks like your car, PJ, is too early, but Jim's car shows the dam just behind the hinge. You can just see part of it. The inserts would clog with debris and were sometimes removed. Also the gaskets would dry up and fall off, so all you would see is the metal tab that is held on with 2 tiny drive nails.