Transmission fluid leak

[dtrojcak]

While towing a small cargo trailer loaded with hunting supplies up a mountain side, my brother's 2000 F350 auto tranny started leaking transmission fluid.
When we cranked back up after everything cooled down, the truck would not move on its own. Went to local Walmart and bought fluid and stop-leak. Next morning, put one bottle of stop-leak and 4 quarts of fluid in. Leak stopped, and we drove it down the mountain and into town to local dealership. They checked it out and said they couldn't find anything wrong. Said there was a vent hole that the fluid might have been coming out of since we were on such an incline for so long. But the leak actually started down in a creek bed where we were relatively level.
We drove home yesterday 800 miles with trailer in tow and no leakage. Is there something we should be worried about or did the stop-leak fix the problem with a bad/weak seal or something?