My truck was sounding like a semi on the highway. I checked rear diff and was low. No fluid dripped out and could not feel with finger.
No signs of a leak?? I added gear lube as best I could. Real mess.
Location of fill hole is horrible. Any one have a good way to add fluid here?

 

There are a lot of oil pumps you can use.

 

I have a collection of dispensers, like condent dispensers in a diner, transfer fluid to dispenser, attache hose and fill differentials. Lot of other uses, but small enough to manuever up into frame to get to hard to reach fill poorts.

 

You can also get a good fluid transfer pump at harbor freight for cheap.