Looks like SAF-XO is designed for cars with an open differential, and is the wrong part number for our limited slip diff.
That's per
Castrol. Castrol recommends SAF-XJ for cars with a limited slip diff. And it's what (or equivalent) we're all using. I don't care what they emailed, open and limited slip diffs have different requirements.
Have them put SAF-XJ in.