2016 Ford Expedition. I changed out the factory fill on the rear diff. a few years ago when it had 50k miles. Put in Delo Gear EP-5 80W-90 with 1 bottle of Motorcraft friction modifier and all was well until a few weeks ago. Now at 100k miles, the LSD started chattering horribly when turning, it was like hitting rumble strips. Did not do it on short trips, but on 20+ mile trips it was bad, especially with a heavy load in the vehicle.
Last weekend I drained the oil and looked it over in the pan and did not see anything unusual. The drain & fill plug magnets did not have anything scary on them either. Refilled with Royal Purple 75w-90 and 1 bottle of Motorcraft friction modifier, and did a bunch of figure 8's in a local parking lot. We have been on a few 50+ trips with it and all is well.