I purchased an old enlarging lens (at least 30 years old) and it had a slight appearance of oil on the blades (all of them).. I have used it for over a year and it still works great, very smooth.
If my experience is anything like the rest, this means no worries..
I do believe it is true after my past reading that >putting< oil on blades is not a good thing to do, have no idea of the real implications of >finding< oil on lenses...
I am sure someone can help clarify!