Malleus
Far west of Siegen
IMHO, it depends on the size of your wallet. There's nothing wrong with using non-synthetic gear oil and, there's a good case to be made that, under normal driving conditions, it's a waste of money.
The only reason to "flush" the gearcase with oil is to remove any contaminants that haven't settled to the bottom of the case or stuck on the magnet. If you follow a regular maintenance schedule and change when you get the diffs wet (I mean under water, not driving in the rain), you'll be fine.
The only reason to "flush" the gearcase with oil is to remove any contaminants that haven't settled to the bottom of the case or stuck on the magnet. If you follow a regular maintenance schedule and change when you get the diffs wet (I mean under water, not driving in the rain), you'll be fine.