1) Despite the Daimler-Chrysler merger, your MB will not shift like a Dodge. You will feel the shifts in your MB. It's supposed to be that way.
2) Use the search feature of this forum and decide for yourself. Lots of reasons to use synthetic and lots of reasons to use conventional. No so many reasons to use semi.
3) Patrick Tan at Mercedes Select Service (935.8533) in Milpitas is very good but mostly a Diesel guy. There's a shop in Campbell but I don't remember the name just now.