Well IIRC, you must first remove the plastic housing on the left wheelwell. I remember it being a little tight but a pretty straight shot with a long extension to the female hex plug. (still talking about cars ) I removed the entire reinforcing panel when I did mine, but you might be able to get away with using the little black door (not for the engine oil drain) to drain the diff.

I'm not remembering any metal lines in the way...could you post a pic?

For the fill, Castrol SAF-XO 75w-90 is what BMW specifies for non-LSD which is what we have. But they don't sell it with containers. Or go down to your Landrover dealer and get LRN 7591 Gear Oil (which comes in containers)...same stuff.