Problems Putting in the selector shaft seal

I understood if the car leaked while not running, the fluid level had to be higher than the leak while running. That points to the dipstick O-ring. Then there is a potential leak area at the pivot pin where it is visible at the back of the case on the exterior. IIRC the 727 had the same issue. trans fluid is some very low surface tension stuff, meaning it can really get into tiny cracks and porous materials.