I think its definitely the port and not the cord, because if I "twist" the plug around by rolling it in my fingers (it's round) the power to the SD3 flickers on and off, like the plug is not making a good connection somewhere in the port. It has to be in the perfect position in the port in order to have power.

Well, if you told me you rotated the board with the cord stationary, then I'd say you could rule out the cord.  But you're there and I'm not, so you'll have a better idea of how things are.

Perhaps blow some air into the hole to remove any dust or other obstructions?

Maybe tape the cord in place to reduce the impact of vibrations?

Could it be a short in the cord itself, rather than the port?

Or perhaps the connection on the board is bent?

Is anything visually wrong (photo)?

nothing appeared amiss, let me check it with a magnifying glass.

I think its definitely the port and not the cord, because if I "twist" the plug around by rolling it in my fingers (it's round) the power to the SD3 flickers on and off, like the plug is not making a good connection somewhere in the port. It has to be in the perfect position in the port in order to have power.

Or perhaps the connection on the board is bent?

Is anything visually wrong (photo)?

Any easy fixes for a non-electrician?