Mav - Just get some metal polish like MAS or Semichrome which you can find in a local Hardware Store and polish off the few stains you currently have. When you switch to the YS 20/20 you will occasionally have the need to polish the muffler from time to time as small brown spots will still appear but not like they would with Castor in the fuel. There is no reason to take the muffler off the Heli to cook it in Anti-Freeze as your brown spots are minor in nature.