Adding ATF to the fuel got started in the '70s, and was proven wrong. Do not add anything to the fuel not created for that purpose. Clean fuel, clean fuel filters, and clean injectors should be all that is needed. That is the way the engine was designed. The products made as diesel additives are OK if you are having problems or feel you need to do something extra. I drove my 300D 23 years and added nothing but fuel. Regards, Ed