[Kajtek1]

There is lot of myths about oils. The viscosity is not parallel with mentioned shear strength.
Than in the case of motor oils, the low cold viscosity actually helps to protect the engine by starting the lubrication on cold start up much faster than the heavy oil, that keeps engine running with no oil pressure for long time.
If the lower viscosity oil is MB approved - I would use it unless I would live in Mojave, or similar location.
New oils, especially synthetics give much better protection, than the old oils even if you drop few points on viscosity level.

 

[Kajtek1]

I placed order with ecstuning last week as well.
They have the lowest prices and carry items other wholesales don't, but than slap you with high shipping charges.
Taking 5 days to ship would indicate that they sell the stuff they don't have in their warehouse.
Can be good deal on bigger order when you have time, but hard to beat autohousaz shipping on the same day.

 

[Kajtek1]

Those differentials take about 1l of oil and even those oils can get expensive, I can't imagine how you can have $40 difference between the brands.
I am admirer of synthetic, but MB differentials were making million miles on dino oils, so going with older specifications should not make big difference.
I think most of the cars in question were filled with dino at the factory.

 

[Kajtek1]

You would not consider sharing some of the stuff for triple what you paid ?