lorenz

I just blew with my mouth at the bottom part of a viewfinder few times then power cycled a camera - and it worked!
No longer see the issue that was annoying me for the last few months  

I had this same issue and tried to insert a thin transparent film between the glass and eyecup, but no luck.

..but blowing compressed air from a can worked. There was no visible dust/dirt in front of the sensor, but maybe there was some dirt between the glass and the eyecup that got blown away.. who knows, but now it works.