Transmission leak on 2010 Ford E-150

On the back of my transmission where the drive shaft connects, there is a black knob (with wires) that twists into the transmission. Does anyone know what this thing is called? It has a nice leak coming from it and I am assuming that it is a gasket.

1 answer 1 comment
electrical bulkhead
Is it hard to replace? I saw a post where it said I had to drop the pan, and replace the O-Ring on the inside. Seems pretty easy. Any advice?