chevy transmission

on my way to showfest my transmission started blowin out fluid, someone said it got hot and blew the front main seal or somethin, i got it back yesterday and realized it was comin from about halfway down the tranny, there seems to be a plug on the pass side about 4-5" down from where the dipstick/filler is, and its loose, we think thats where its comin from, anyone know what the heck that thing is?