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