Can I make a recommendation.
If you've read another post by a member giving away a R200 diff for FREE, because he cleaned it out with WD40 and sometime later opened it up and noticed that there was a ton of RUST inside it. Kind of like a foamy rust.
http://forums.hybridz.org/showthread.php?t=143524
If I were you, in the interest of saving that machine, I would suggest not to use WD40, and use a better cleaning agent, or make sure you oil everything down afterwords.
I know WD 40 stands for Water Displacement 40th formula, and it should keep water and rust away, but oil will protect better.