So after almost a month I have just received my D750 back from Nikon service after the issues I was having with what I believe to be oil spots on the sensor.
They serviced the camera, including cleaning the sensor, and stated they had found and fixed the fault. I have just done a quick test, same as I did before the camera went in, to visualise the spots on the sensor. This was shooting an A4 piece of paper at ISO100, F22, out of focus and using the visualise spot tool in Lightroom.
See below for before and after - I am not impressed with the cleaning job. Whilst it is better, I still wouldn't expect all these spots, and what appears to be a smear on the right hand side. What are other peoples opinion?
Going to have to monitor it after putting some more shots through it.
Before Nikon Service by
Phil Scott, on Flickr
After Nikon Service by
Phil Scott, on Flickr