I call mine "old oily" but she is a beast, a frame eating beast, I just love this camera. I love my 5D4 but the 1DX2 this week for me has been a beast, with focus priority, BBF, Servo focus this thing just rips, it gets shots I never thought existed, oil issues aside I am proud to own such a camera, but, I get you 100% and my issues were posted on here the day the 1DX2 came out.
I don't go out to look for sensor issues on my 1DX2 or any other body tbh, if I see issues on my shots I will address them, but my (number three) 1DX2 has been problem free, I did have a couple of pre order bodies that had dust on the sensor, only seen at f22 but Canon replaced them from new (well Wex UK did after talking to CPS) my problem is I just can't part with the camera, I did early on say sod it, got my money back and moved on, but then a month without it I gave in and got another, eat some humble pie and went out shooting. Shame you've had such ongoing issues, I'd fear checking mine stopped down!
edit: I just remembered I did change the focus screen on mine as it had specs of dust on, they would not shift with a blower so rather the hassle I just changed it for a new one, dust gone from the viewfinder and life is good again. I hate dust, even one bit haha