The mb 235.7 gear oil specification applies to fuel economy hypoid gear oils with viscosity SAE 75w-85, 85w-90.
Replacing your Mercedes Benz gearbox oil is usually a straightforward task, if you're reasonably handy. In fact, replacing gear oil is normally a very similar process to changing engine oil.
Running a high quality gear fluid not only ensures smooth gear change but is vital for the protection of internal components and gear faces / teeth. Even if your Mercedes Benz states it's fill for life, you'll quite often find it still has a drain and replacement timescale in your handbook
If you're unsure if MB 235.7 is correct for your vehicle, or have a modified or unique Mercedes feel free to get in touch for a custom gear oil recommendation.