2017 NEWMAR DUTCH STAR Unknown Or Other Problems

I OWN A 2017 NEWMAR DUTCH STAR MOTOR HOME ON A FREIGHTLINER CHASSIS. THE DIESEL EXHAUST FLUID (DEF) SENSOR (DEF HEAD) HAS FAILED TWICE. THE FIRST FAILED AT 14,795 MILES AND WAS REPLACED ON 9/24/18. THAT HEAD LASTED ANOTHER 15,000 MILES AND FAILED AT 31,218 AND WAS REPLACED ON 11/25/2020. EACH HEAD LASTED ABOUT 15,000 MILES OR 2 YEARS. THE PART IS MADE BY SHAW DEVELOPMENT WHICH HAS NOT ANSWERED REPEATED ATTEMPTS FOR INFORMATION. AS PART OF THE EMISSIONS SYSTEM, FREIGHTLINER HAS REPLACED BOTH HEADS UNDER THE 5 YEAR FEDERALLY MANDATED WARRANTY ON EMISSION SYSTEMS. CUMMINS (WHICH MAKES THE ENGINE) ALSO IS INVOLVED IN EMISSIONS. THE THREE SEEM TO PASS THE BUCK FROM ONE TO THE OTHER LEAVING THE CONSUMER TO DEAL WITH THE SAFETY ISSUE OF DERATING AND COST AFTER THE WARRANTY. WHEN DEF SENSORS FAIL, THE ENGINE CAN GO INTO DERATE WHICH IS 5 MPH. THIS PROBLEM IS...