yes it has a cork gasket IIRC
thats were you get at the snap ring that hold the tail shaft on
I like to clean them down good with brake clean the air dry with airgun
I then throw a hand full of baby powder arounf the shift levers,dip tube,pan gasket,and the one your asking about..let sit over night,should help pin point it and wont have the blow back to make it look like its something else
also look at the back were the tail shaft goes on..ther is a pressed in shaft that the servo lever is piviting on that will leak back ther as well
jack rear of car up and clean with brake clean,dry,cover with rtv and let cure