A group of us are finding a substantial amount of water in the differential cases. The vent lines are sucking water in. We are going to try to relocate the lines to a higher spot. I'll advise as to how it works.
Here is a tip. I ride in alot of mud and am obsessed about oil. I have already changed my diff oils about 6 times now. Something I noticed, if you check the diff anywhere from right after to an hour after you have ridden it.. it will look milky like you have water in it. You need to let it set unshaken for about 5 hours and it will return to its normal clean greenish color. If it still looks creamy after that then yeah you have water.
I agree with Duramax. If it look milky at anytime, there is water in it that does not belong. It will seperate after 5 hours and fool you. Skake up a container of gear oil and look at it; it may have suspended air bubbles in it for a little while but it won't turn white and milky looking unless it is some strange stuff.
I am going to reroute my vent lines this weekend. If you search the site, Someone just did a whole instructional thread complete with pictures about a month ago. I can't remember who it was.
I too have the same problem. It is only the rear diff. Anytime I go through any water, I am changing the rear diff fluid. No problrms with the front though. But I will be doing all of them at the same time I do my stealth snorkle.