I’ve had a stubborn spot on the sensor of my Nikon D7100 for awhile now. I could not remove it simply by blowing air at it.
I did some reading online (in particular this detailed article), and went out today and bought a pack of Sensor Swabs preloaded with Eclipse fluid. I was a bit hesitant, but followed the instructions.
The first swab didn’t do it, but a second swabbing appears to have dealt with the annoying spot.