RockAuto has a new one for the 2004 SLK320 ( same as ours ) for $69 no core :
More Information for POWER SELECT/WPS 17852N

A OEM Bosch will set you back around $250, the el cheapo above has a 12 month warranty, the Bosch has a lifetime warranty.

You decide ( would you put a cheap *** starter in a fighter jet ? )

Personally, I'd do the wire fix I mentioned in the previous post and call it a day.
( If you don't want to mess with the soldering, you could always drill and tap a hole in that plate and use a double eyelet cable )