I don't have Super 8 2T, but do have People 50 2T and Super 9 LC. Both those oil tanks have a marker inside the tank that shows where the tank is full and it's a little below the top. Look around on the black plastic near the fuel and oil openings and you will probably find a message explaining how to tell when oil reservoir is full. It's probably not obvious, but after you see it, it will make sense.
Take something and suction some oil out. You have probably overfilled the oil tank and it will leak until you use up enough oil to get it below the point where it's spilling over the top while you are riding. That's my guess. Cheers