If you look up into the bell housing, several of the pump bolts will be visible, behind the torque converter. If you see signs of any ATF, the leak is most likely the pump gasket/O-ring, or the torque converter seal. In rare cases, I've also seen the converter drain plug seal leak, so it's worth a look. If this area is dry, the pan gasket is obviously the next thing to check. Keep us posted.