2001 Ford Windstar transmission leak

We took our van to get the transmission serviced before going on vacation. It was not leaking at all. We picked it up and drove it home and it was leaking really bad. By this time the shop was closed for the day. We called the next morning they sent a tow truck to pick it up at our house. Later in the day we got a call from the shop saying the only leak they could find was the front seal and it wasn't their problem. We cheecked the fluid. It was full. We have been home several hours and it hasnt leaked yet this time. What could be the problem or what do we need to do?