I have an issue with my Canon 5D shutter. Roughly every fifth photo, the shutter doesn't quite close properly (about 5% open at the bottom of the sensor) and the mirror stays open. The screen shows Error 99. A second press of the button for about half a second will get it back (it won't record that photo). Turning the camera off also gets it back. Now, I replaced the shutter curtains about 5 years ago with ebay replacements after they failed. It worked well for a year or so of occasional use. Then the camera sat unused for several years. Coming back to it now, the shutter has this issue. I could go through the whole shutter replacement again, but that was a lot of work, and the camera is probably not worth the cost of a new shutter. It's certainly not worth a professional shutter replacement. I've been through all the standard error 99 testing, switching lenses, cleaning contacts, etc, etc, etc. The only thing left is the shutter. I wonder whether lubricating the shutter might help - if the shutter is dragging too slowly, maybe that triggers an error in the camera? The shutter isn't fully jamming - it seems fine, and it quite able to recover without any problems, and then runs fine for the next few shots before jamming again. Any suggestions, or is it time to retire the camera?