I would check around the shifter shaft seal very carefully. The fluid level rises as the convertor drains over a few days to a level above the shifter seal and trans fluid will drip down to he pan rail and then run along the front of the tranny and may look like a pan gasket leak or front seal leak. The shifter seal can be replaced with the tranny in in the car. Some people like to drop the valve body, but I have done it with the tranny intact, but dropped the rear cross member to lower the tranny for better access.