Some have used pressurized air to blow it out. It is quick and easy, but has some interesting side effects. Most just use Q-Tips. However, there are other things that may be causing the appearance of oil on the fins. A loose spark plug (have seen this a couple of times) or lil Johnny decided to help out dad a bit by doing some oiling for him (seen this too).
A picture is worth 1,000 words, here you may get more.