The 300E and all other "older" MB models were made to run on dino oil. The only advantage you would get with synthetic is you get a longer oil change interval--but who cares when your paying about $5 a quart for synthetic. Trust me, save your money, and use dino--perfectly ok. If on the other hand you purchase a brand new E55, I would suggest using synthetic. New performance cars need synthetic due to its technology, blah blah.
Catrol GTX--$1.49 a quart at autozone--you cant go bad...
Monotoned Smoke Silver
97 Style Replica E420 Rims 205/55/16