I too own an LR4 and I'm in the process of tracking down the perfect D5. Since my LR4 does not have HD package, my first challenge was trying to figure out how to tell if a D5 has a locking rear diff so I can absolutely get that this time. At first, it was simple. Check Topix. The report will very clearly indicate "REAR AXLE ACTIVE LOCKING DIFF". Then Topix got locked down and now charges a fee for everything. Not wanting to waste money every time I saw an interesting D5 listing, I started research. And it think I figured out how to tell, visually.
First, the vehicle needs the Capability Plus package. The package also includes ATPC and Terrain Response 2. If the listing says it has that package, you're all set. If it doesn't or you want to visually confirm without paying for Topix, I believe I've found a way. How? The cluster of buttons in the center console area. If a vehicle has ATPC, there will be a split button in the bottom left corner. Vehicles without ATPC, thus without Capability Plus/locking rear diff, will only have a single button.
In short: Capability Plus = locking rear = ATPC button present
