Drivers side Brake light out?

OK, the description of what you have done points to the bulb socket assembly itself as the problem. To test if it is the issue unplug the connection to the socket, take a simple test light and touch it between pins one and three in the socket (Black wire and Red wire with black stripe) Have someone step on the brake, does it light up? If yes, the socket is bad. Replace it and you should have a working light.