D800E "sticky" aperture control / autofocus issues

It's been awhile since I've taken my D800E out for active duty. Given that it's the heaviest camera body in my arsenal (especially when used with an F2.8 constant-aperture zoom lens) and takes up the most space - I only reserve it for when quality absolutely matters.

I brought the old beast out for today's photoshoot (you can read about it over here), and, should I say, fortunately, everything was fine for the entire photoshoot. It was at the end after we called it a wrap, that I noticed that 2 things were amiss:-

1. I was not able lock autofocus on anything - the camera basically just kept cycling from infinity and minimum range, before stopping at infinity.
2. The viewfinder was really dark, even at F2.8.

Of course, the first thought that entered my mind was a combination of disappointment and dismay. My past experience with Nikon camera repairs had not been commendable (nor affordable).

After I got home, I systematically tested my camera to verify the problem was repeatable. Swapping lenses, found that the problem persisted, so that basically confirmed the problem was with the body itself.

Tried to remove and reinsert the battery - but that did not solve the problem.

I tried resetting the D800E, which was done by turning the camera on and then holding down both the Qual and the "+/-" buttons (marked with green dots on the body) for several seconds. Unfortunately, that didn't help either.

While contemplating if and when to send in the body for repair - I unintentionally hit the depth-of-field preview button a few times. After a couple of cycles, the viewfinder suddenly became bright again! Along with that, my autofocus ability returned as well.

Breathing a sigh of relieve, I guess that shooting at a constant aperture of F2.8, the aperture control tab must have gotten stuck as the camera stopped down while I was taking some outdoor shorts in P mode. That would explain the viewfinder being dark - which in turn was too dark for the autofocus system to work. As this is something related to the in-camera aperture control, even mirrorless cameras will be affected.

My take from today's experience - have to remember to periodically exercise all mechanical systems, hopefully to keep them from jamming up due to lack of movement.