Stainless power venter flue

As I was installing power vent motor this fall I noticed my stainless flue was showing areas of surface rust (outside end) I packed flue in off season with papertowels and seal with plastic on inside of basement. Is there anything I can do next Spring when shut down like spray with anti corrosion oil?. I did not think stainless flue would rust? Thanks in advance for any advice.

I sprayed it all with oil at the end of the year, looks ok.