In the rear oil is delivered to the pinion bearings by a scraper/cup attached to the pinion support.
In front applications the oil scraper/cup will not be there as it would block oil flow because the gears are turning in the opposite direction. There are two different oil fill level plugs depending on front or rear application. The lower plug is for stock rear applications and the higher plug is for front applications. ALWAYS fill your diff to the NON-reamed out fill hole plug.