There is a rear differential leak in my car.
Hello. A rear differential leak is something that requires immediate attention. If the fluid continues to leak, it could cause the gears inside the differential to start rubbing metal to metal. This will cause premature failure of the differential. It would be much cheaper to fix the leak than it would be to replace the entire rear differential. A certified technician, like one from YourMechanic, should come and inspect your vehicle and make a recommendation as to the necessary repair which hopefully is something as simple as a seal replacement.