Is it safe to buy a used D600? Did Nikon fix the oil splashing issue at all or is that something owners of D600 have to live with forever?
I've never owned nor used a D600, but most of the reports I have read indicate that after extended usage the problem more or less goes away. Of course the oil/dust already on the sensor, which is actually on the IR filter in front of the sensor, must be cleaned. But after the initial 'break-in' period as the excess is slung off of the parts that it was applied to there is less and less oil/dust that needs to be cleaned.
Here's Roger Cicala's blog entry about the D600 dust issue written in October of 2012. Be sure to read all the way to the end for the addendum posted in July 2013.
Here's a follow up entry Roger posted in November 2012.
I have a Nikon D600, and have had it warranty "repaired" by Nikon UK 3 times so far.
Each time I have only had between 300 and 400 actuations on the shutter mechanism before having to return it. I've just received it back again from the third time so I will have to see how it works out.
The issue does seem to have been less noticeable each time but perhaps I just noticed it sooner being sensitive to the issue.
It became extremely noticeable at the smaller apertures like f20 and higher. The worst bit was that out of the 8 months that I've had the camera, it's been away for repair for nearly 3 months combined.
If you can see the camera before buying it, take an image at f20+ of a blank wall and zoom into the upper-left quarter of the image. If there is oil you should be able to see it just using the camera rear screen. Setting the colour settings to monochrome can make the spots more noticeable too.
Yes, there is a risk but is minimal. The problem as it is known on the D600 is solvable by wet cleaning. You can do it yourself or factor-in the cost of sending it to Nikon when you consider the used price. If you are lucky, the D600 in question may still be under warranty and while it is not always officially transferable, they rarely ask more than proof of purchase, so ask for a copy of the receipt from the seller.
Indeed that means that you may be buying a camera that shows more dust than typical and I did notice that with one of the two D600 that Nikon loaned me. Dust did appear faster than usual but after a few weeks, it did stabilize.