Another Rear Differential

[f5fstop]

Yes, take it back. If filled properly, it cannot be overfilled, since you fill to the bottom of the fill hole. Adding more fluid only pours out of the fill hole. If it was only on the diff, I would say they were just extremely messy, but since it appears to be all under the rear of the vehicle, it appears fluid is being forced out and spraying on the bottom of the vehicle.
However, not impossible to put a seal into the housing incorrectly. They did something wrong.

Is this the same dealer who rebuilt it the last time? And the same dealer who said the EBTCM did not pick up the rear wheels speed sensors being out of adjustment? Mmmmmm