My C280 wheel offset is ET37 but I want to put a ET40 on it. how can I do it without any rubbing issues OR can I even do it all?

any info is appreciated. thanks

 

If you are going to a narrower tire like from P225 to P215 you shouldn't have any problem. If you will be using wider tires you may run into interferences, MB has the wheel well tight to the wheel. If you want to use wider tires you may want to get a wheel with a smaller offset that pulls the wheel to the outside thus eliminating the possibility of interference with the wheel well or front tires at turns. It makes them look better too.
All of the above is true if you are keeping the overall diameter of the wheel the same. That is 2 X Pxxx X Aspect Ratio / 100 + Wheel Diameter in inches X 24.5 is the same or close before and after the change.