You can clean and re-pack the grease on the splines.It should be self evident when you get the wheel off.You can download a manual from this good forum links as well,
http://cx500forum.com/The Hypoid oil type is embossed on the side of the Drive box.It only takes a little and I change mine when I change my oil as a bottle of Hypoid goes a long long way on these bikes.
You use the small bolt to drain and the 17mm Large one to fill.There is also a grease nipple on top of the box that you put 3 squirts of grease in at the same time.
More info here,
http://www.pdsrecording.site90.com/cxgl ... Change.htmThe gear shift seal can be prised out with a flat blade screwdriver and then a new one tapped in.Best done if you drain the engine oil or drain bit as it will seep out a bit if the oil level is normal.
Please put whereabouts you are as it make's it easier to give specific Area/Country advice for parts etc.