Check the front of the trans, around the countershaft hole. That is where most Muncies tend to leak. As there is no gasket or sealer around the front of the case.
If your leak is actually from the front bearing retainer. You can make a gasket from simple cardboard material ( I use Rice Crispy boxes!). A little silicone sealer and you have no more leak.
If the trans is leaking because it is just hanging in the car. Just raise it to level.. There is no actual front seal on the input shaft, only a slinger. Overfill will also cause leaks. I used to make up a paper gasket to cover the entire front of the trans and glue it between the trans/belhousing. This will stop pesky countershaft leaks also.