My car is operating correctly but I recently found this on the underside of the car. I don’t know if what I am looking at here is simply something that got splashed on by the road or whether this is a blown gasket or seal or what. I took a swipe at is with some cloth and it is oil/grease not transmission fluid. There are no other signs of leaking anywhere on the car or on the ground.
It looks like the seal is smeared and deposited on the smooth surface of the inner axle - the smooth surface that should be farther into the transmission, surrounded by the seal. For some reason the inner axle is not fully inserted into the trans. It should click into place, and stay there. All lengthening and shortening of the drive shaft should be taking place within the inner CV joint.
Personally, unless its a new car, it’s not something I would be concerned with at all unless it gets worse. To repair it requires pulling the axle out, then replacing the seal and putting it back together. I gotta believe the labor is in the several hundred dollar range. This would be something you do if and when you ever need an axle or it starts to drip transmission fluid. Others may disagree though, but to me its not going to hurt anything.
The OP could try pushing the axle farther into the trans. It might click into place with a good shove. Then the only problem is a worn seal and possible leak. Same as now.
BTW, pretty good detective work finding this problem! Had the axle ever been pulled, say, maybe while putting in a new wheel bearing or hub? Maybe it was never pushed back hard enough to set it in place.