Truck Repair: transmission leak, chevy 350, th400 transmission

Question
I have a 1976 Chevy 350 with a TH400 transmission that has recently been rebuilt.  It is leaking transmission fluid out of the transmission into the odometer cable connection and on to the ground.  Should the cable connection encapsulate the fluid or should there not be any fluid getting into the cable housing in the first place?
Thanks for your help.

Answer
Hi John,
That gear and shaft is just splash lubricated, and there is no seal there that I know of. However, if the transmission vent is plugged, pressure could build slightly inside, and force fluid out through there.
Vent should be on top of tranny.
Van