trans pan leak battle

I had a similar problem on a 727.....Changed out the gasket a couple of times with no avail. Finally had enough and took the tranny shop to do the gasket. They changed it and it leaked, put anew pan on and it leaked, changed the shifter seal and it leaked. As it turns out there was slight wear (barely noticeable) in the shaft that comes up through the seal. They changed that, and problem solved. Just my experience. Good luck.