I've got a refurbished EM-1 that I purchased from Olympus back in Feb. It's been having issues with the rear dial. When changing settings (aperture, shutter speed, etc) it intermittently responds. A slower turn is more likely to work than a faster one.
After shooting a ton on a recent trip, the issue appears to be getting worse. Called Olympus, sounds like it could be a bad button. Will likely end up sending the camera in for repair.
Wondering how prevalent this issue has been? Googling the issue turns up lots of others with similar problems.