What Could Cause Transmission Fluid To Leak

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I'm leaking transmission fluid from the middle section of my van. There is a little puddle. I guess it is the seals but what else could it be and what should I do put alot of transmission fluid in there and drive it to the mechanic. I just got it back from him after he put a cable in, 'cause it wasn't shifting right. It wasn't leaking, before I took it there. donna_rdly@yahoo.com