Hi, Paul,
The later higher HP starters have a hot terminal on the starter solenoid that can be used to bypass the ballast resistor.
The 230 SL original starter does not have tis extra terminal.
If you want to bypass the resistor, you have to add a relay wired to the coil side of the ballast resistor so that it gets the full 12V when cranking.
If your car starts OK now, maybe you don't need it?
Naj