Windage can make oil get there.. As you are driving...Pluss the oil drops down from wind to rearward parts. Leaves you thinking that its where its coming from..But it can be further forward from where it appears to be leaking....The "frustrating" part is rear seals can be wet or very slight leak [which is o/k] and something else can make it "seem" worse..apita..
I have had similar problems with a couple of falcon autos. What can happen is the internals of the rear of the box floggs out , you can throw as many seals at it as you want it wont fix it, the g/box guys do a mod (fit a bearing i think) into the rear section where the driveshaft enters then a new seal . All up $150 - 170 nz ,