Speaking of Powr-Lok break in (which no one was, but who's counting), Jaguar released an interesting service bulletin back in the early 1960's specifically advising
not to do the recommended differential
oil change at 500 miles if you had a Powr-Lok (which they had always prescribed up until then). Now, if you've gone to the trouble of having your Jag rear diff rebuilt by super-pros then, by all means, follow their directions for break in and not a 50 year old service bulletin.
I don't think they even had climbing gear lube back then much less friction mods specified by today's rebuilders. Regardless, here it is should anyone ever ask you about it, which they won't.
