Common Tranny Leak Spots?

Go buy a couple cans of spray brake cleaner. Get under the car with an old tshirt and clean everything up. Then leave it sit overnight. A leak that big, will most likely show itself, without the car having to be started.
Be mindful that brake cleaner will slightly swell the dipstick o-ring, stopping a leak, at that spot, for only a day or two. I just did this with my truck and found the dip tube to be the culprit.