Quote:Not bad, you need a longer lens
What are you shooting these with?
The oil issue is caused by an internal flaw in the camera, I believe, so leaving the lens on will not help you with oil. Using only one lens will be a pain and isnt worth the reduced risk of dust. But the less time you spend with the lens off the camera (without a body cap), the less likely you are to expose it to dust. Always take the lens off with the camera body pointing sensor down and change the lens quickly, youll be fine for quite a while.
Oil may not even effect your camera. If the problem does arise, I recall hearing that Nikon was doing free servicing for the cameras to fix the problem if you take it to your local dealer.