So I've had this same question for a few days since I stupidly allowed a friend photographer talk me into swapping out a focusing screen with crop marks that he had, with mine, so I could shoot a family and keep them in the crop lines for a canvas wrap print.
His intentions were good, but I probably didn't need the screen swap for what I was doing.
Anyway, since then, the dust has been bugging me, I've removed the focusing screen and used my rocket blower down in the camera and on the focusing screen as well. Didn't help. I have even used a lens cloth on the focusing screen too, sometimes made it worse, sometimes helped but not 100%, I'm wondering after reading some of these posts and links, if I've ruined the focusing screen now? Is it that sensitive that I can't/shouldn't touch it with a lens cloth?
It doesn't appear that I've done anything, when looking through it, other than move dust parts around. Can I squirt some lens cleaning solution on this thing and wipe or swab it to try to remove the dust particles? Or should I just take it into a camera shop now and have the entire process cleaned (sensor, mirror, focusing screen), the works?