Just called a local Mercedes-Benz dealership parts counter, with the same parts number as shown in your picture, and I was quoted $27.50 per bottle.
I had to lie and pretend that my car is a C63 AMG Performance Package :P And even then, they don't even know which car that part number is for
So to be sure, I have to "bring it in"
Imagine their surprise when I DO show up....
Locally I was charged $22 for Redline 75W140 gear oil for my 2 annual rear differential fluid changes. I have had no problems with it for 2 years, but if the Castrol is cheaper from Mercedes, I'd do that. Since it's not.... I'll see.
Oh, forgot to mention that the local BMW dealers do not sell bottles yet, still drums. This is Vancouver, BC.