All limited slips require an additive. The outboard braked rear that I have in my car is based on the Salisbury Power-Lok and requires the Amalie LSD additive, which is hard to find, or the GM additive, which is easy to find. But you absolutely, positively have to have an additive in there or you get sticking, ratcheting, and other rear end misbehavior.
Here is an interesting link dealing with the Jag rear leather and rubber seals and their compatibility with
synthetic gear
oil (and
synthetic LSD additives). As always, take with a grain of salt.
XJ-S Final Drive