Here's how I change the transfer case gear oil. I put my jack under the bike and raise just enough to make the bike level.
Then remove the large plug on the side of the case cover, I use a large washer held by vise grips to get it loose. I then remove the drain plug it's on the side just below the big plug.
Then I tilt the bike slightly towards the drain hole so I get as much old oil out as possible.
After that is done install the drain plug, and just below the large plug there is a small screw (allen head - I can't get a pic of the small one my pipes in the way) remove that and with bike level pour new oil into big hole until you see it oil run out the small hole, Transfer case only takes a small amount 0.4L (0.35 imp qrt. 0.42 us qrt). it is at the correct level then.
Put small screw back in ,then the large plug.
Your done !!
(Paul- TenFeathers)