M273 engine OK, but may have known sprocket wheel problems.
Mercedes had to deal with a court case because of this.
M273 a much updated development on the M113 design, with 4 camshafts (not 2) and variable valve timing, a bit more economical and powerful.
I am looking for a C209 coupe CLK500 , with a 5.5 M273 engine, but it HAS to have an engine number of more than #8612, to avoid the sprocket wheel problem, but that as right at the end of the C209 production in 2009.
Could very well turn out to be a futile search.
Although CLK 500's with the 5.5 litre M273 engine were produced in 2009, I don't think that any were sent to Australia in 2009 or 2010.