Powerglide leaks fluid 2 days after racing
 

I have a pretty well built powerglide with aftermarket 180 gears, trans brake, recently rebuilt. It never leaks trans fluid while racing / running, but a couple days after, I will see a large area of trans fluid on the floor, with no indication where it came from. The pan gasket is sealed, the lines do not leak, the convertor seems dry. Any ideas?

Could it be draining out of the cooler and running out the dipstick tube?

Check the vent. If clogged, pressure will build and push fluid out.