The following are links to the major manufacturers of synthetic motor oils.
First, there's AMSOIL's Marketing Manager's personal webpage.:
http://www.cp.duluth.mn.us/~ennyman/a-pages.html
Then Mobil DelVac 1.:
http://www.mobil.com/mobil_lubes/onhighway/products_services/delvac1/index.html
Then RedLine.:
http://www.redlineoil.com/whyredline.htm
Finally, Lubro-Moly's parent company website. Note that they make a synthetic diesel oil, as well as a regular diesel engine oil and even a 0W40 multi viscosity oil.:
http://www.liqui-moly.de./ani.htm
As far as commercial trucks and what they use, there is no factual comparison to be made of Mercedes diesel engines to Detroit, Caterpillar, and or Cummins commercial diesel engines. But for the sake of information exchange, most heavy trucks use Larry Bible's favorite oil, Chevron DELO 400. Many owner-operators have changed to DelVac 1 for the fuel economy, extended drain interval, ease of starting in low-temperature climates, and reduced engine wear. The only reason to not use DelVac 1 in your Mercedes is that it can be hard to find an outlet for you to buy it from. Heavy trucks change conventional motor oil every 15 to 30 thousand miles depending upon how they are used. Cross-country driving allows for the longest change interval, as the truck is being used more, and operated at a steadier constant road speed. Mobil claims that for long-haul trucks, DelVac 1 allows for an increase to 60,000 miles. Again, a comparison of diesel trucks to our Mercedes vehicles is ludicrous.
Another benefit to consider in using synthetic oil is that it contains no wax, or paraffin to combine with combustion by-pruducts and form sludge. Also, it helps to combat the formation of acid that results from the naturally occuring condensation of water vapor produced during the combustion process. Add to that the better detergent properties of the synthetic, along with the increased lubricity, and your engine will last longer, run better, stay cleaner inside, and will have less wear in the long run. But I would only change the oil filter when you change the oil, and not before.
I also recommend you buy the best diesel fuel with the highest cetane rating that is available to you in your area, add a proper fuel additive like Redline Diesel Fuel Catalyst, or 85+ (same thing, different label), you will increase your fuel's cetane rating, and it will burn more efficiently, thereby reducing the amount of soot produced by combustion, and accumulated in your crankcase. Mercedes Benz diesel engines require much higher cetane fuel than is generally available in this country.
My '82 300SD has had Redline or Mobil 1 synthetic motor oil in it for the last 80,000 miles. It also has Redline in the transmission and the differential. The owners manual recommends a 5,000 mile drain interval when using conventional motor oil like Castrol. Redline has told me that I can safely extend that to 15 to 18 thousand miles when using their synthetic. I have decided to stay with the 5,000 to 7,500 mile drain interval for the time being.