check the fluid level to make sure its not over filled. could it be something else like the pan, if you over tighten the bolts to the pan the gasket will leak, lol, not tight enough will do the same. have to get the surfaces clean and straighten the pan if needed so its not all bent around the holes before installing.

 

Sometimes the seal become hard over time and they wear grooves in the shaft they are suppost to be sealing. The shafts can be swapped out.