Tranny leak.

I put a new (well not new but new to me) transmission in my car. I adjusted the clutch cable today and thought i should check the fluid in the transmission. So when i get the car up on the lift i noticed that the bottom the the transmission was wet. I'm pretty sure that fluid is leaking out of the tranmission on the drivers side axel. I'm pretty sure that theres a seal that goes around where the drivers side axel goes in. Does anyone know the name of this seal i am thinking differental seal ??
Anyways i had to add more fluid to teh tranny and i filled it up to where my finger can touch it if i put it in hole, is there about how much you need. If the axel was pushed all the way in would it casue it to leak ??

Anyone ??