The throttle body is MUCH cheaper.
Go to Car-Part.com--Used Auto Parts Market
choose 2004 mercedes sl series, then throttle body.
on next screen choose a 230 type ( these are the 74mm TB's, you have a 68MM OEM TB )
The 74 will directly replace the 68, better high RPM torque, and actually better MPG's

Call the yard and make sure the part number on the black plastic cover is 113 141 0125