I'm not sure about Mercedes seatbelts, but I work for Nissan and the seatbelts we supply the latest models with all have a haz-mat label and are vehicle specific.

Also, you will have to investigate the tongue (shiny part) size and shape and see if it's compatible with the 2005 Mercedes parts. A lot changes in the auto industry in seven years... Especially since we're using post-facelift R170 components, which puts the technology at over ten years old.