Common Tranny Leak Spots?

Hey guys, I have a tranny leak that I need to find and decide if I can fix it or not. When I bought the car in May the fluid was about a pint low but the guy I bought it from said it didn't leak. I filled it up and it had a slow drip while I worked on some other problems. Took it out to some friends, we found that the tranny pan was pretty loose, so we tightened it up and it seemed like it wasn't really leaking anymore. But, at this point it was about a quart low, so just a couple of days ago I filled it up to full before going out for a cruise. I got home, check under the car after a couple hours, and it seems like no leak. But, next morning I check, and there is enough fluid on my cardboard that a puddle has formed. Checked today and there is even more fluid. This is a pretty big-time leak. Anyways, is there a kind of leak that can happen only when the car is cooled down? Could the transmission be getting too hot and making a leak worse over time?

Also, I have been putting Dextron/Mercon fluid in it at the recommendation of the previous owner, but i saw at advance they had ATF +4 fluid which said it was for Chryslers, should I be using this?