gear oil getting from sm465 into 205 case

[mudmizer]

My plan is to go to an automatic but after having gear oil blowing out from the vent tube for quite a while I started to think that somehow it must be over full. I pulled the fill plug and drained 2-3 ouarts untill it stoped running out. I then checked the tranny and it was WAY low,scarry low. I guess a seal or gasket is out between the two. The tranny level was well below the coupler part of the adapter so I guess it's leaking through the lower part of the adapter.
Any ideas as to what I'll need to replace, I guess all the seals and gaskets as long as I split the two. Is it possible to leak between the two or is somthing broke?
It may be a while before I can get the auto ready to go in.