WHAT   TRANS   ???? 

There is no seal listed in my parts book for the transmission output shaft if that is what you are looking for on a 3 speed transmission from 32-36. There are gaskets/shims for the torque tube ball at the rear of the transmission. If you are having leakage it ., most likely is from the torque tube ball area. If that is the case there are parts available from vendors to make a repair.

I agree with Steve that your problem might be the gaskets and shims in the u-joint ball housing assembly.

The reason for no seal at the back of the tranny is that oil from from the tranny slowly makes its way into the u-joint area to help lubricate the speedometer gear, the u-joint trunnions, the u-joint splines connection to the drive shaft, and ultimately the front bushing/bearing in the torque tube. Then, the oil drains into the rear end.

This is a slow process, but over time, you might find that you are filling the tranny, and removing a little oil from the differential. 

Dean