Why not buy the genuine part from the eBay seller from Lithuania?I double checked on a US site and they are selling a genuine mercedes shock compatible with e350, e550, e63 with option code 489 (active suspension).
Part number is Genuine Mercedes 2123201630, A2123201630 Shock Absorber; Rear Right - Mercedes
On the Miessler site they say that the shock is compatible with that exact original part number - 2123201630
I'm hoping this works out!