Fountainhead

I changed my diff oil at 12K or so. I knew it didn't "have" to be changed, I changed mine because it was fun! My diff oil had a lot of suspended material in it (was not clear as new), and the diff plug had ferrous material on it also. I've never changed the diff oil on any car I've owned (or truck) but I did so on the Z for the first time. The drained oil actually looked dirty when it came out. I didn't change the fluid to prevent damage.