Buying A Repairable Vehicle That Has Hazardous Materials In it

2003 Ford TBird Convertible Top Fixed. Now Transmission is going out. Where to get parts? Should I use Diesel Fuel Additives and is it important? What about buying Hazardous Material vehicles from Recyling Yards. Changing Transmission Fluid on a 2016 Ram with filter in the pan. What causes a 93 Ram 1500 engine to not start? 2014 Ford F150 Missing Air Dam is it important?