That is a sad story. It seems you have had an unusual problem with oil or dust. In 14 months of ownership, I have cleaned the sensor 2 times on my D7000 and it is clean with no dust or oil. When I change lenses, I usually do it in the least dusty place I can find, hold the camera lens mount down and keep the time between lens changes very short.
My experience with a Canon 5D MIII was not so good. It seemed to attract dust. It went back to Canon dealer for good last week due to really poor AF and AE. So I am finding the D7000 (and my D800) to be much less problematic.