Here's the original diff from when I retro-fitted my M Performance LSD:
The part number actually faces upwards, away from the road surface, when the diff is
in situ. It can be read with difficulty, apparantly, either by using your mobile to take a photo or with a mirror.
This is the standard diff part number label close-up
For such an important part, you'd think BMW would forge or laser etch the LSD part number or something on the case, to indicate it's an LSD.