As in bama ramblers post, take the drain apart, clean off old putty on the inside of the sink side (if there is any) and use plumbers putty under the lip of drain inside the sink. I have seen a few with rubber gaskets but I would still use the putty (remove gasket). Get a ball of putty and roll it into 1/4 'rope' that will go all the way around the drain lip.
Scott and Liz - Southern NM
2012 Wildcat Sterling 32RL - w/level up (best option ever)
2007 Chevy 2500HD 4dr short bed Duramax w/allison
Reese Fifth Airborne air ride king pin coupler with Sidewinder