A good question to be asked here is what kind of vehicle and diff you have.
A three-gear ball differential type absolutely gets no lube at all except for a dab of silicone grease inside each ball hole. Sealed spyder diffs can accept different weights of heavy oil to control the slip of the differential action. This is more for traction fine tuning than lubrication.
There are other differentials, with other lube notes, but first we need to know what type of diff.