ATF, ATF everywhere

[smashingchuck]

Alright guys and gals, I've got a bit of a conundrum.

I put the 87 together about 6 months ago, but still haven't plated it for the the street. The trans (TH350, which was built new about 5 blocks away) has been rebuilt and has about 15 miles on it.

Here's what is happening. I put the trans pan on, and everything is fine. No leaks at all. I can go for a drive, and still no leaks. I can let the truck sit overnight, start it up, drive it, no leaks. but then after 2-3 days of the truck sitting, BAM, 3 quarts of ATF on my nice clean driveway. At first I thought the pan was the culprit, so I bought an aluminum pan that would not distort when i put the bolts in. I thought that fixed it until 3 days later there it was leaking again.

I can't really see where the hell it's leaking from... other than the pan area itself. my cooling lines appear to be tight.

Ideas?