A few months ago I had a spot on my KM 5D sensor. It would not blow off with air. I borrowed an Arctic Brush and that did not get it either. After a lot of research I purchased some "Visible Dust"cleaner and swabs on line.
I read the instructions, took a deep breath and wet cleaned my sensor.
It worked perfectly. It is not really a difficult task if you follow the instructions and have a steady hand.