filling the differential on 2000 Avalon

I have a 2000 Avalon XLS. I've just completed a transaxle fluid replacement and in my enthusiasm decided to do the same for the differential. Having drained it, I now find that the fill plug is not where I anticipated it to be. Diagrams [Haynes, Camry forum] all have it located facing the drivers side wheel, rearward of the drive shaft and slightly below the level of the drive shaft. There is a casting location right there but it has never been drilled or tapped so it's not like anybody sheared the bolt off. Does anyone know what I'm missing? I'm assuming that the differential doesn't draw fluid form the transaxle. The only other thing that looks remotely possible is a strange cap-like assembly on top of the main differential body. It looks like an exaggerated figure eight profile.The casing is milled flat with a 3/4 to 1 inch cap is held in place with a 10 mm bolt. It'd make gauging the fill level tricky though. Should have checked the fill plug first I guess, before draining it.
Thanks.

After a brief early morning chat with a technician at my local Toyota dealer, it turns out that the ever reliable guys at Haynes were the problem. Although the guide states 1998-2001 model year, the diagram and instructions are for a '96 differential. Although there are still two drain plugs, its a common fill operation through the dip.

cheers

Thanks for the update. I couldn't figure it out from the manual. :)

The auto transmission is the whole diff. Atf fluid about 3.5 qts.