Leak test will tell you.
How much oil are you putting in, it should be no more than 650ml.
Trans oil can get out three ways, leak from case, blow out the breather or pass by the crank seal into the crancase.
If it is leaking from the case or coming out the breather you should see it.
If it is passing the seals it will be evident as the motor will blow white stinky smoke.