Leaking 904 Transmission.

I bought a 1973 Dodge Dart Sport about 9 months as ago. The transmission started leaking just drops of fluid a few months ago. It's progressively gotten worse over the last few months. It seems to leak more when sitting than it does when driving. I stopped to get gas the other day and cleaned off the windshield and also waited a while before driving away. I'm that time I looked under the car and saw no leaks. I've searched this site and found some posts talking about leaks but nothing about my same situation. Do does anyone have any idea what I should look for? Any help is appreciated.