Just changed my rear diff fluid on my '04 LS for second time at 94K. Fluid itself was fairly clear, not too dark. Plug had a bunch of grease-like sludge on it. But weirdest thing was when I removed fill plug, it hissed like a soda can, and didn't smell great. Sure sign I waited too long?

I've always bought cars new and overmaintained them, keep them for 10-12 years, 120-150K. Mostly GM. This car is in such a class by itself in terms of quality and reliability that I've kind of let myself believe the factory rec re maintenance intervals. No more. Diff and trans will get changed every 30k from now on.