yes, torque ball is the most likely source for leakage at the rear of an Dynaflow.
These torque ***** seem to have a mind of their own. After highway driving with oil hot and thin they keep tight and after sitting for month in a cold garage afterwards with the oil being thickened by the cold you can find a puddle...
You will never know without determining the source. Wash the transmission with brake cleaner as good as possible, start the engine and look where the oil comes from.
As I said: Torque ball is likely, but since it is quite a job to get the transmission out there you probably wanna be sure you do not have to look for another seal also.