My car has almost 7000 miles on it. When is a good time to switch to synthetic oil. I used Mobil 1 in my 97 Cobra and planned on using it in my 01. Also, is there any advantage in using fluid upgrades such as Royal Purple in tranny and rear end? Has anyone used the Steeda or Fluidyne radiator upgrade. Claims are that it lowers the temp about 10-20 degrees. What injector gas treatment , if any, does anyone use?