Aeorostar transmission leaks up top soewhere when hot or under pressure

I have a 91 ford aerostar van. XLT rear wheel drive.4.0 liter. When it gets warm or hot. Usually after a hard shift and always from just driving around town when not driving like a perfect old lady. Its leaking from the top somewhere, yes the fluid levels are good. I dont know if its a vent and if a basic trans. Service would work. The shigting and transmission seem to be running great, unless it runs dry of course. Is it the seal? Upper seal? I know its not the pan. To Im hoping we can just have the seal replaced. Someone stated the torque conv. In the tranny may be going bad and causing overheating, Its a 91 and if not a simple venting issue or just a seal leak, I dont want to dump 2 much $.I just need it to get me to school and work for about 3 more months