Hi gang, I've had my D3 a bit over five years now. Last year it developed a focus problem. Sometimes I'd lift the camera to focus on something, press AF-ON, and nothing would happen (I long ago shut off focusing with the shutter button, and the camera's always on continuous focus and release). Other times autofocus would take place at once. Sometimes I'd lock on to something, track it, and the camera would lose focus part way through the tracking. Sometimes it would stay locked. It wasn't a lens problem because all my lenses were focusing perfectly with my D800. It's not an AF-ON button problem because I switched shutter focus back on and tested with that for a while. No change.
In early December the problem became severe enough that there were more misses than hits with the D3, so I sent the camera to Nikon for repair. Got it back yesterday. The situation's improved but the problem's not gone completely.
I'm not sure whether or not to send the camera in a second time. Happily I have a couple months to make that decision. Has anybody else had the problem I'm having? If so, what was the final outcome?