I had a bit of transmission problem on the way to Atlanta from Orlando. What should've been an 8hr. trip turned into 13. I was leaking tranny fluid at an astounding rate. I had to pull over every hour and attempt to fill my tranny with fluid using a water bottle. It was fun.

Anyway, after ariving in Atlanta at 4am in the morning, I started to make phone calls to find someone who could fix this on a Saturday. I found an Isuzu dealer who took pity on me and my vacation. Dropped the truck off and had to blow 3 hours. When I picked it up, the dealer told me I had a cracked torque converter cover (I think that was it). It cost $180 dollars to fix. Thing is, I changed my oil the day before I left and I didn't see any fluid leaking or anything cracked under the truck while I was under there. How the cover cracked, I have no idea. I imagine any tranny shop would be able to tell you what's leaking. Just for reference, mine was leaking exactly where you described, between the oil pan and tranny pan.

Good Luck!