Spoke again with Nikon on the D600 oil/dust issue - A fix is on the way! Locked

If there is a significant problem with a significant number of D600's lubricants to do with moving parts in the mirror box area could reasonably be the cause.

"Ordinary dust" is not the likely cause as the "clean image senso"r menu option removes ordinary dust.

dpreview, who use cameras a lot while testing, reported more marks than normal after 4 weeks use. By looking at the dpreview images you can make your own mind up as to whether the top left of the sensor had significant marks after 4 weeks heavy use.

I would be surprised if parts with too much lubricant need replacement rather than cleaning. Time will tell.

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Leonard Shepherd
Many problems turn out to be a lack of intimate knowledge of complex modern camera equipment.