When I receive the new control unit I propose to dismantle the camera and try relaxing the screws and maybe lubricate the other parts of the current control unit before attempting to install the new unit.

I read in another post for another Nikon camera, that someone relaxed the screws that hold the aperture control unit together and that made it work. Could it be a result of poor quality control that a number of 5300 units suffer this problem?

Alternatively, a new aperture motor control unit is only $14 from China, I just wonder if it would solve the problem?  

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On the basis that they are also readily available on Amazon,  I have decided to buy one and see if that solves the problem.

I have a similar issue with my D5300.

Small aperture settings create the shutter error and are cleared by switching back to automatic mode and persisting with the shutter button.

Problem occurs with both my lenses on the D5300 and the lens works perfectly on my D70s.

Tried all the things you have..

Took a series of shots under the same conditions but reduced aperture successively. At about f6.7, the exposure dropped dramatically which matches my experience under normal shooting conditions.

Repeated the experiment on the D70s with the same lens and no dramatic drop off in exposure, it behaved as expected.

In desperation, stripped the camera down, found nothing untoward inside, put it back together but still get the same press shutter button error.

It still shoots fine photos at wide apertures but anything above f8 can cause problems.

One interesting observations is that the onset of the problem is delayed at longer focal lengths.

Did you resolve your problem and if so how?

I have a similar issue with my D5300.

Small aperture settings create the shutter error and are cleared by switching back to automatic mode and persisting with the shutter button.

Problem occurs with both my lenses on the D5300 and the lens works perfectly on my D70s.

Tried all the things you have..

Took a series of shots under the same conditions but reduced aperture successively. At about f6.7, the exposure dropped dramatically which matches my experience under normal shooting conditions.

Repeated the experiment on the D70s with the same lens and no dramatic drop off in exposure, it behaved as expected.

In desperation, stripped the camera down, found nothing untoward inside, put it back together but still get the same press shutter button error.

It still shoots fine photos at wide apertures but anything above f8 can cause problems.

One interesting observations is that the onset of the problem is delayed at longer focal lengths.

Did you resolve your problem and if so how?