Found this, looks like you fill the box from underneath through a plug in the pan, looks like the diff uses a different oil supply also.
Steve.
1) Remove drain plug. Drain ATF. Install NEW seal on drain
plug, install and tighten to 30 ft lbs. (40 N.m).
2) Remove ATF inspection plug. Using ATF Fill System (VAG
1924), carefully insert fill hose through an opening in the deflector
cap. See Fig. 2. Ensure deflector cap is not pushed out of position.
Fill until ATF runs out of inspection hole.
3) Shift selector lever into park position. Start engine.
Press and hold brake pedal. Shift through all selector lever positions
with vehicle stationary. Shift to park position. Check fluid level.
Add as necessary.