Diff fluid change interval

[Hal]

While we are discussing oil life and change interval, I wanted to revisit the differentials. In a previous thread it was briefly touched on but the discussion focused more on the T-case fill procedure and the diffs were all but forgotten
[ http://www.elcovaforums.com/forums/s...ad.php?t=20941 ]

I changed my front and rear diff at 10k miles and found the rear diff oil noticeably black while the front diff was not bad at all. What does the manual say? I couldn't find any clear answers, but I'm glad I changed mine when I did because the rear diff looked pretty bad, and I think others here have found the same thing.
Whadayallthink?