<200Q> Differential drain plugs

[Hans-J Tannenberger <hans@sequent.com>]

Hi,
first of all my sunroof is fixed thanks to the help from Joe, Igor
and Andrew. Thanks guys.
Next project. I'm going to replace the transmission oil with
redline MT90 and the rear differential with redline 75W90 GL5 on my
'89 200Q. I had very good experience with redline on previous cars.
I checked the car and found the drain and fill plug for the manual
transmission without problem. I do have a 17mm allen wrench :-)
The center diff has only a drain plug. Does it share the oil with
the trans, i.e I open and close BOTH drain plugs and fill with ONE?
I don't want to get the center diff dry without any means to fill
it up again.
Second, the rear diff has two plugs at the bottom, I imagine
one is the drain the other the filler plug with an internal
pipe to stop the oil from dripping out while refilling.
Am I correct, if yes which one is the filler which one the drain?
My book from the '86 doesn't cover quattros :-(
Again thanks in advance.
- Hans

'89 200Q
'86 5KCST