Which differential oil?

[Decolliber]

I have a 2002 530. I believe that BMW uses/recommends Castrol SAF-XO or SAF-XJ (if limited slip differential), which seem to be available only from delaler service departments.
Does this car have a limited slip diff? I think not, but am unsure.
Is it encessary to use the dealer supplied gear oil or could I just use Mobil1 75w90? It has nearly identical specs (density, viscosity index, etc) according to manufacturer web sites.

[632 Regal]

if the M1 is the same weights than it should be safe to use, non synthetic is a no-no.