I now use Mobil 1 (0W40) for my ML350. Works great here in the winter as well as summer.
I purchased the car from the dealer last year and they were using Quaker State syn.5W30. When I asked why they do not use a superior oil like Mobil 1, they said I would have to pay an extra $40. See link below to choose the right oil if you want to use MB1.
Check which Mobil 1 oil is right for your vehicle
Don't even think about using that oil in a Mercedes diesel with a DPF, unless you want to plug a $3,000 catalyst with ash!
Diesel oils have specific detergents that clean the motor aggressively in the first 1000-3000 miles hence the rapid darkening instantly after being replaced. In fact you should be concerned if it did not turn black since this would indicate a weak additive formula not intended for diesel applications.
That detergency cleans the motor but it also prevents the high pressure wear additives from bonding with the metal during this period. After approx 3000 miles this detergency cycle ends and the dispersants take over preventing the soot from forming large conglomerated particles. Typically with correct oils the soot remains in the 50-500 nanometer range even after 30,000 miles of continued use. Oils have to be tested at 8% soot and run for 500 hours to meet the specification. After 20,000 miles of use you will barely reach 1.5%.
Do not change the oil any earlier than 10,000 miles. You want to run as long as possible after that initial detergency cycle to reduce the total wear on the motor.
Only use the Mobil 1 5w40 ESP Formula M, this oil is a top tier version that has some of the best wear reducing additives available. The oil is approved out to 20,000 miles, but MBUSA due to pressure from the dealerships slashed it to 10K and 1 year.
I run our Bluetecs out to 2 years and 10K, once they hit 40K I'll be running 2 years and 20K (as I do on the CDI) between oil and filter changes (supported by oil analysis results, not some wild guess).
The engine air filter will not need to be replaced unitl 60K or 4 years. Don't worry, the ECU monitors actual filter condition, so if it is anywhere near restricted it will trigger a service on your cluster. Best advice leave them alone until called for, early replacements result in more dirt ingestion due to loading. The longer they stay in service the higher the efficiency at trapping dirt...up until they hit the max service differential which is 30 hPa.
The fuel filter is replaced every 20K, so your next service will require a fuel filter (very easy to do).
The only thing I would recommend looking into is if the brake fluid has been replaced. It should be virtually clear, if it is dark or a darker shade of amber you may want to consider replacing it. Never use a dyed brake fluid since this will discolor the brake reservoir and prevent you from determining the color and condition of the fluid.
Tire pressures, I have found that optimal wear requires about an extra 1-2 psi in each tire based on the full load pressures. More than likely the monkey checking pressures set them incorrectly, the rear tires require HIGHER pressure, the fronts lower pressure due to more heat generated on the fronts. This allows the tires to equalize in pressure and provide proper grip for correct handling with the ESP/ABS systems.
Don't leave the engine idling, this is not good for a modern diesel...don't confuse these with a CAT or International, then again those auto shut down after 5 minutes....so maybe you should!
Transmission fluid and filter will also be due at your next service, read up on it and be ready. Also you may want to pull a sample and have it checked. If these are used in city driving you will want to reduce those intervals by as much as 50% based on wear metals being generated.
Its a great engine you'll love it!