How to fix leaking skeg box?

I took my QCC 600X to the QCC factory in Exeland WI to have the skeg repaired. The good news: the skeg works better than new. The bad news: the rear hatch nearly filled with water during an eight mile paddle.

Looking for advice on diagnosing and repairing.

Even better (since I have no idea how the skeg box is put together), does anyone know of a repair shop in the northern Virginia area?

A quick way to diagnose is to flip boat
over and fill the skeg box with water and observe where it leaks.