gearbox drain plugs?

[PATRICK_KELLY@HP-Andover-om3.om.hp.com]

Item Subject: Text_1
     I just changed the rear diff oil on my '87 5kSQ thanks to some advice 
     from the Q-list on where the fill plug was located.  I used the plug 
     on the bottom of the case directly below the half shaft to drain.  
     There is another plug about 18 inches forward of that drain which I 
     did not open.  When I went to do the gearbox oil last night I found a 
     similar set up, one fill plug level with the half shaft, one drain 
     plug below the half shaft, and another drain plug 18 inches back near 
     the driveshaft. Why the 2 drain 1 fill setup or am I missing 
     something? Will the oil drained from both plugs be refilled through 
     the single fill plug?
     
     TIA,
     
     Patrick Kelly
     twin '87 5kSQ's 
     
     P.S. Someone on the list was wondering about this model of non-turbo 
     quattro. Mine have the large aero headlights, 130hp NF engine, one 
     silver, one maroon so I don't know about the white. I believe this 
     model was only made in '87 and '88.