After my first go-karting I noticed a tail shaft leak out of my 4R70W automatic. So I e-mailed performance automatic and they mentioned that the AOD driveshaft yoke was smaller diameter than a 4R70W yoke and they've had a couple FFR customers with the same issue. I assumed it was the seal. So instead of a $3 seal, I got a new $165 yoke and got it installed last night.

AOD Yoke from FFR diameter - 38.05mm
4R70W yoke from Performance Automatic - 40.55mm

Size-able difference, but at least the leak is gone now! Thought you would like to learn from me.