If you opt to change you gear oil in the rear diff, be sure to remove the fill plug (upper) first. Reason being, if the upper plug is stuck/stripped and you cannot remove it, but have already removed the drain plug (lower), you now have no way of replacing the oil. Very simple procedure:
Pull upper plug, position drain pan under the diff, pull lower plug. If the rear diff is warmed up, it will drain out in about a heartbeat or two. If stone cold, it may take a minute or so. Allow to drain as long as you can (an hour or more,even overnight [right Larry] if you're not in any hurry), then replace lower plug and top off with 2 quarts of your favorite hypoid gear oil.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.