The seal is leaking where the driveshaft goes in the differential

Just to be clear, you are seeing a leak at the flange for where the drive shaft bolts to the rear differential? If this is the case then you need to remove the driveshaft, pinion flange and change the seal out. Here is a guide that will help with the driveshaft:

https://www.2carpros.com/articles/how-to-remove-a-drive-shaft

Below you will find the process from the manual on how to replace the seal. Let us know if you have questions but this is not the easiest seal to replace but can be done in a driveway. The only issue is setting the proper preload again on the pinion.