The problem with the dye is, unless the fluid "piles up", you may not pick the dye up with the light. In other words, if the fluid is on a flat surface, like the transmission case above the rail......say coming from the dipstick tube or shift shaft seal, you will have a difficult time spotting it, because it is spread more thin than if it is in drips on the pan.
Have you gotten a mirror and looked all along the top of the pan rail at the dipstick tube and shift shaft seal areas? At this point, I would leave no stone unturned. It's obviously leakin somewhere.
