The pinion seal is leaking from the rear differential.
Hi. The pinion seal leakage is a pretty common problem on older vehicles with differentials. It is generally a pretty inexpensive repair. Lack of fluid can be catastrophic to the differential so it is recommended that the leak is fixed as soon as possible. I suggest having a technician, like one from YourMechanic, inspect the leak because there are other seals on a differential which are prone to leakage as well.