I had a similar problem from a mile o matic 59 Edsel trans gave it a service and put the right amount of fluid that the workshop manual said I don't go off the dipstick as I found it not to be accurate enough , since I done this service it has been fine ever since
I used a piece of 1/4 rubber fuel hose , sat in the groove nice an tightened up well no leak as yet and the car has been on the road for over 12 months now
Paul