The transmission is from a 1983 W123-300TDT (USA version).

After replacing the bearing of the pump, see here:
http://www.peachparts.com/shopforum/diesel-discussion/311580-722-3-transmission-pump-bearing-damaged.html
I proceeded with the assembly of the oil pump. I pressed in the seal. The seal was bought from MB:





I used two pieces of wood and a vice to press it in. I also replaced all the seals of the oil pump and put in a new gasket for the oil pump housing.

Installed the torque converter, with the aid of these two metal strips, it installed correctly, the transmission was held upright during installation.



Installed the transmission, filled it with 4 liters of ATF and started the engine. No funny sounds. Put in another 2 liters of ATF and I tested the transmission. There was power to the wheels, but unfortunately there was also a large puddle of ATF on the floor, coming out of torque converter housing.

There wasn't time yesterday to remove the transmission and inspect, we have to do that tomorrow, but I would like to know what the possible causes are before starting the work. And I like to know what I did wrong, so I will not do it again.

The amount of oil suggests to me that it is pumped out, so there is probably a problem with the front seal. Did I install it incorrectly? Maybe the flat piece of wood made the seal "flat" too and maybe a large socket should have been used. The FSM has no special instructions or tools for pressing in the ring.

Could it have been damaged during installation of the torque converter? The seal seemed sturdy enough and the torque converter went in smoothly.

Any ideas?