Gear oil is not just gear oil anymore. The limited slip additive is a friction modifier for the clutches to help eliminate groaning during cornering. It is only recommended if necessary. The main thing you need to look for with Jaguar differentials is that it meets “Hypoid” specs. I have seen gear sets galled from improper lube used. Most of the better gear oils that are listed with GL5 specs have this but it usually says it on the container so best to check. I also recommend the heavier weight gear oil for the Jaguar diffs. 85W-140 for example. As there is no filter or cooler (other than the later finned covers), the oil gets pretty thin when hot so if you start with a thin oil, it gets really thin when hot.