I fixed this same problem on my Dad's 300e this summer. There is a large o-ring that fits between the tranny case and the front pump. It is a 4 dollar part, but the only way to change it is to drop the tranny out of the car and pull the front pump. The o-ring was cracked all around the pump. It took me about 8 hours to pull the tranny, change the o-ring, and re-install the tranny. It is now dry as a bone. Some people also warned me that the front pump could chew up the bushing where the torque convertor rides, but mine was fine.