Technically last night, but I changed the fluid in both my front and rear differentials and the transfer case. While I had it apart I installed a new cover on the rear diff and used a LubeLocker gasket when I put it back together.
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This was my first servicing of the diffs and transfer case since buying the Yukon. The rear diff fluid looked fairly clean, and had been serviced before at some point. Only a little metal dust on the magnet. The front diff appeared to have never been serviced in the 160K on the vehicle. The fluid was dark and opaque. The magnet was covered in a thick layer of fuzzy metal shaving, but no metal chunks or chips.
The transfer case fluid looked clean, but the big surprise was about a quart of extra fluid came out when I opened the fill port before draining the case. A little research suggests that I have a bad input shaft seal on the transfer case and ATF from the transmission is making its way in. I always check the ATF level before I head out to tow (it's on our departure checklist) and have never seen the level drop. I'll keep an eye on it now since the level in the case is where it should be, I'll see how long it takes to loose a quart of ATF. I guess that's another thing to add to my to-do list.
Any thoughts or suggestions on how and when to deal with the transfer case seal are welcome on the thread I had going here:
Servicing Transfer Case and F/R Differentials - Fluid Recommendations?