Get under the car (with jack stands) clean the area up, run the car and see exactly where the leak is. Sounds like it's your output shaft seal. It can be very critical ie, tranny fluid leaks out, tranny goes dry, tranny gets hot, tranny melts down, new tranny costs lots of money. New seal costs around $10. Don't go for a discount seal either. The switch is very simple and takes under an hour. Remember don't get under the car without jack stands.
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