My jeep is a 2004 Rubicon. I've had it ~4 years. I did fluid changes all around when I bought the Jeep. Since then, for various reasons, I've changed the oil 2 more times. Each time, the front differential oil is dirtier than the rear. Yesterday, I pulled the differential cover to look inside. Everything I saw looked OK, but I couldn't really see the internals of the locker. The inside of the housing and gears was coated with a black residue. The magnetic plugs had some goop on them, more than I would expect given the oil changes I have made. The front has had some significant use in the past 2 months. Lots of low range and some locker action. Operation has been trouble free except for a thumping noise I get occasionally at full steering lock (axle not locked). When I first heard this noise, I thought it might be the front axle u-joints binding a full lock. That is not what it is. I believe the noise is coming from the axle locker mechanism. Maybe the locker isn't full disengaging at times. I cleaned everything inside the housing with brake cleaner and put in some new oil. Maybe the cleaning will make the difference. I'd like to hear your thoughts and experiences with similar problems.