Changed out the gear oil last night in my f and r diffs. Old oil looked OK, but I had alot (like maybe a teaspoon or so) of a very pasty, oily "sludge" on the drain-plug magnet. It was black, and very smooth and pulverized. Didn't appear metallic, though it did adhere to the magnet. I have fairly new ARB lockers and ring and pinions in the diffs, and I'm wondering if these are sloughing off material as they wear in? This is probably the 4th gear oil change since the new components, and I use high-quality stuff. As far as I can tell, everything is working well...gears run cool and quiet, lockers engage/disengage perfectly. Any ideas?? On a side note, I had a b*#ch of a time getting the drain plugs out, as I had banged one too many rocks on the metal rim thats suppose to protect the plug. The rim folded over to the point that I couldn't get a socket on the bolt. After alot of prying and a few hits on the socket with a BFH, I got everything apart. Replaced the drain plugs with hex-head ones...10mm. I'd recommend this to all before you bugger up yours like I did.