tranny leak

[almadroog_7]

I have a leak on my 1984 300D transmission
It is on the passenger side at the line that connects the transmission to an area near the radiator.

When I unbolted the 19mm bolt i did not see any o-ring of any type on the other side. So i matched a small o-ring to fit on the Outer Dia of the bolt and squashed it in there, but that did not work.

Is there supposed to be an o-ring there?
What is the best way to fix it?

thanks,

almadroog_7