What you actually saw was not rust but dried pretreatment overspray due to lack of maintenance. We see this on occasion on machines where the customer has not done any scheduled maintenance. The SpeedTreater spray valve, for instance, is made of stainless steel. Dried pretreatment spray turns brown and looks like rust on the surface of the spray valve. A little cleaner rubbed on the valve easily takes any dried overspray off and the valve is shiny again.
CoorsDTG makes a great point that any piece of equipment requires maintaining it according to manufacturers recommendations. By the way, please let the person who showed you his pretreater to contact us and we can get him up and running.
Harry
Equipment Zone