If the D7000 was getting lube, when it was not specified and has no lubrication points on the very long list of preventative maintenance and mirror box replacement instructions, that might be an issue of an assembly line change order that never got into the documentation. I do not have a service manual for a D3 but the D2x series did have PM lube points. The advent of better materials has probably meant that need for wet lubricant has been eliminated in all current cameras. I have manuals for the D50, D70, D200, D90, D5000, D2x and D7000, SB800, SB600, and SB900. I also have a service manual for my old Canon A1 that I don't have any more, which like the D2x, had lube points. For me, old manuals are more of a collectors item than old cameras. The image is not just reversed top to bottom but left to right also so the spots are on the physical left side, and towards the bottom. Gravity might not be much of a factor as electrostatic charge. The D7000 sensor has a lot more signal activity per dimensional unit so possibly a electrostatic repulsion system might be a useful addition as a clean-sensor feature for future high density sensors. Static attraction of the particles would tend to be concentrated in the regions of the sensor that had the most dense signal paths. There are just so many possible causes of the dirty sensors, but from talking to D3 owners, cleaning is needed a lot less often with the d7000. One of the reasons oil is not likely the cause is the range of spot size. None are large which would be expected if some mechanical throwing was involved, the spot size is constrained to a range of limited variability. Try oil on the end of a surface and flip it towards black construction paper and you will see a wide range of spot sizes, and an occasional large one far larger than the average. Seeing how the mirror and shutter are made, it is hard to imagine how some reservoir of fluid would accumulate and meter itself out slowly over many months. Since most owners reporting the problem had its first occurrence months after acquiring it, a problem at the start of its life seems less likely. The size range, and higher density in the center sure looks closer to pollen or spores, and the fact that the individual spots do not change shape. But then, at this point it could be anything, Nikon only says it is dirt and not oil.