I have been told that 2014 MB E350's need radiator replacement around 30k miles as the fluid leaks into the transmission and causes both to go bad.

Hello, even if this were true, it's kind of interesting that your vehicle is eight years old with no apparent problems. I don't really see any reason to do any kind of proactive preventive repair. Perhaps check with a second source, another repair shop or even a Mercedes-Benz dealership to see what's going on, if there is any historical information and so on. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops