Often, the leak in the area you describe is on the threaded body of the drain. The mack gasket is too thick and not soft enough, to "reach into" the threads. The easy solution is to take it apart, and smear plumbers putty onto the threads, such that in essence the threads are all filled with putty. Then put it back in. The putty helps the washer seal, and prevents drops of water from traveling down the threads.
Unless there is a crack or defect on the bottom of the sink, that surface should seal. Just in case, you can add silicone caulk, to the bottom of the sink and let the mack gasket bed into that.