From MB site:

Hypoid gear oils contain a high level of EP/AW additives (Extreme
Pressure/Antiwear) and a highly viscous base oil to prevent seizure
when the hypoid gears mesh (mixed and boundary friction
conditions) and to ensure a high degree of protection against
wear. The compatibility with radial shaft seals is regarded as
critical with such high concentrations of additives because the P/S
additive systems become thermally unstable at temperatures from
130 ∞C to 140 ∞C and this may lead to sludging of the hypoid oil.
The resultant deposits on the radial shaft seals then generally lead
to thermal overload and this in turn leads to leakage in this component.

The tooth engagement conditions of the hypoid gears result in a
high proportion of sliding and a low hydrodynamic proportion of
tooth engagement between the pinion and ring gear. Due to the
high tribological load compared to adhesive wear (seizure) and
pitting, the performance of hypoid gear oils must be particularly
high with respect to these types of wear. The formula of the oils is
therefore determined by a high concentration of EP/AW additives
and a highly viscous base oil. Alternative oils, e.g. engine oils,
cannot be used for these drive types. Proof of performance that
an oil fulfills the requirements of Daimler AG is provided by
internal tests. However, the hypoid gear oils must at least
correspond to the US military specification MIL-