Two things... First, that your brake master cylinder went dry & you refilled it, and that air can also get into the system via a leaky master or slave cylinder, means more than likely that in addition to the leak, your brake lines also have air in them. Air in the lines means your brakes not work very well even once the master cylinder has been refilled.
Then, you basically only have five likely sources of the brake fluid leak. The master cylinder and the four slave cylinders at each of the wheels. It shouldn't be difficult to see which is leaking by simply looking at each location for leaking brake fluid. So once you locate the source of the leak, you'll need to replace that master or slave brake cylinder, or perhaps just tighten one of the brake line nuts if you're lucky.
Once the leak is found & repaired, you'll then have to bleed all of the brake lines.