I MUST be doing something wrong

Perhaps if you couldn't return purchases as easily and had to have your D600 sensor cleaned two or three times you might now have a D600 with a clean sensor and no 'green tint'?

Maybe people who live in places where they don't have return policies (and read the internet less) have more 'working' D600s?

('green tint'? If it displayed it that was probably a residue from the curing process which would have dissipated in a few weeks on its own)