Oiled blades can effect the performance of lenses and can be corrected in most cases. Always bring your classic, expensive lenses to a qualified lens repair shop (if you can find one!). For less expensive or less rare lenses you can try it yourself if you are handy with a screwdriver and take care with it.
Don't get confused between oil on the blades and fungus. Fungus can spread to your other lenses and lenses with this issue should be isolated from clean lenses.