Here are the emails of my story:
Me: It should be your responsibility to pay for shipping when you sell a part that isn't made for the vehicle in question.
RockAuto: I have called CENTRIC to verify the fitment of this part for you. If your vehicle is 2003 MERCEDES-BENZ C32 AMG 3.2L V6 Supercharged, the CENTRIC Part # 13035027 that you ordered should fit, and definitely should have the 4 ports. We are not able to cover return shipping for a part that the manufacturer verifies should fit if that is your vehicle.
If your vehicle needs a part with 3 ports, though, the technician suggested that your vehicle may not be an AMG and instead could be a C230/C240/C320, but he cannot verify without a VIN. If that is the case, you may have simply ordered incorrectly for your vehicle, and he suggested the below part for the different model. If you provide your VIN, we can pass that along to CENTRIC for them to verify.
Me: I don't make mistakes when ordering parts. The vin number for our 2003 Mercedes C32 AMG is as follows: WDBRFXXXXXXXXXXXX
Today I ordered the correct part (3 threaded ports) from my local Mercedes dealer part number 005-430-98-01
I suggest you remove CENTRIC Part # 13035027 from the list of components sold for a 2003 Mercedes C32 AMG and cover the shipping costs.
RockAuto: I called CENTRIC again to double check the VIN, the model of your vehicle, the part as it is listed, etc. They even list the OEM #0054309801
as a direct cross-list to their part when I asked them to run it in their system. I was advised by the technician that often there are 4 ports total and one is plugged on the car, which may be the case with your vehicle.
Whichever the case, we do not have enough information to state that this part is listed incorrectly and that the catalog is incorrect. Typically we do not cover shipping either way in this type of return, but I am willing to make an exception for you and cover one-way of the shipping, since the part is obviously not fitting your car and you have successfully replaced it. Would you prefer we refund you the original shipping or would you prefer that we send you a return shipping label?
Me: Centric is incorrect. The OE Mercedes master cylinder on a 2003 Mercedes C32 AMG does not come with a plugged port, the extra plugged port you're referring to doesnt exist at all because of the casting. I'm not concerned about the money I spent for overnight shipping, this is about the principle of your company doing what is right in this situation which you have failed to do and in doing so you have lost my future business.