Passat differential - add oil?

Help! I recently replaced the driver side output shaft seal and o-ring on the differential. All went well until I needed to add the 90 wt gear lube. There is only (as far as I can find) one fill/check plug that is on the passenger side.
Does this fill for the entire diff? Not the autotrans but the diff? The diff is completely drained I cannot get it to accept any oil. As if it is full. Maybe the gear lube is too cold to drain into the diff?
Any help would be appreciated as I am at a loss.

Thanks!

The plug next to the right side (passenger) drive flange is indeed for the diff. The only special note is to take at least 5 minutes to fill it after service so the oil can settle. Maybe you can try spinning the wheel a little bit in case there's something on the differential that's in the way.

Thank you, I will give this a try.

I pull the VSS and fill from the top.

-Todd

Todd, a great idea! I wish I would have thought of that. Thanks much for the help.

I fill all my VW transaxles this way. Pumping it in from the side always makes a mess.

Make sure to use a lube that's safe for yellow metals. I use Pennzoil Syncromech.

-Todd