oil plug seal

There are a couple things that could cause this so it's hard to say why this would happen. Did you buy the o-ring from the dealer? Is it a rubber/silicone style o-ring or is it a copper washer? Did the bolt appear to go in straight and did the bolt head seat flat against the pan? Do you think it was cross threaded? Did the mating surface look damaged or beat up in any way? I don't have a torque spec, but is it tight enough? Obviously you don't want to over tighten it but the plug still needs to be snug. If it were me, I would look at how the drain plug looks tightened in the oil pan. Then I would clean around the drain plug with some brake clean or carb cleaner and inspect exactly where the oil is coming from (from between the mating surface or possibly a crack from overtightening). Depending on what I found I would give the plug another 1/8 to 1/4 turn or something else. Assuming no damage to the pan or plug, and if tightening didn't help, I would take a trip to the dealer and buy the drain plug seal. Are you sure the old seal was removed prior to installing the new one? That can definitely cause a leak the same way having 2 seals on the oil filter can.