Check out the diesel forum on mbz.org. If you'll look on the archives, there has been numerous and verbose discussion on the merits of Synthetic vs. Dino Oil. Mercedes also has a list of "approved" engine oils which they have published. I'm not sure about Amsoil, but I know that Rotella does NOT make the list. Also, be very careful when purchasing synthetic oil as recent changes in advertising regulations have allowed manufacturers to sell an oil as a synthetic when the majority of the oil stock is actually mineral oil.
Mobil 1, Amsoil, Bardahl and a few others are the only "true" synthetic oils available.
I, and many others on the MBZ.org forum have had good results utilizing Mobil 1.