Excess fluid in tailshaft

It is filled to the filll plug dribbles out.
3/4” below the hole - there is no room to check that. Read the service manual.
But yes- 80w90 is acceptable over atf in manuals but a leak is a leak. it’s the yoke, bushing or seal..... or all together.
it’s a 50 year old car. Chances are it’s worn some. Lo!
Syleng1