I did mine a while back. It was for maintenance purpose only, since I did not know when the last oil change was. I did use hypoid gear oil (one full bottle). I do remember that it was a bi*** to get both plugs out. I got the fill plug out first, then the drain plug and lastly the vent which is located in the top rear of the differential.
Good luck!

__________________
J.H.
'86 300E