Looks awfully like dirt on the sensor to me. Have you used a hand lens 'puffer' or had a look at the sensor (or it's covering filter) perhaps under a stereo 'scope or even with a hand-lens?...Your images really don't look like dead pixels to me, more like a dirt/dust particle...
Bull's eye, John B.!
...So - finding the bug quest
0. Puffed the front and back of the reducing lens (again!) - black dot persists.
1. Rotated the reducing lens relative to the camera - black dot persists.
2. Removed the reducing lens and inspected the camera - a few tiny dust(?) parts revealed. Puffed them away.
3. Black dot persists. A bug - dead pixel - in the camera?
4. There appears to be a filter, it is glued to the back side of a retaining thread ring. Luckily, although I do not have a pin spanner or compass, the retaining ring and attached filter were easy to unscrew, with a pointed-tip forceps. Took out the filter and puffed front and back on it.
5. Inspected the bare camera sensor chip through the stereoscope - looks nice and clean.
6. Puffed the chip without touching it, several times.
7. Reassembled the apparatus and back to the microscope.
Now what about the bug? Here is a real one (aphid) from a flower.Black dot gone. So, it had been dust. Perhaps shaped as a pixel...
Thanks folks for the help!