iSight not recognised in iMovie, launch Daemon .plist missing, won't rebuild.

My system is working fine (iMac running Mountain Lion), except that when I try to import video to iMovie '08 using the built-in iSight camera I see a message "no camera connected". iSight works fine in Skype, photobooth, etc.
The solution to this, documented here, is to trash com.apple.mio.VDCAssistant.plist at the path /System/Library/LaunchDaemons/ and it's supposed to rebuild after a restart. But when I navigate to this path, the relevant file is just not there. Restart doesn't affect it, neither does logging in with a different user account. Repairing disk permissions doesn't help. I found a file named com.apple.cmio.VDCAssistant.plist at that location but only in a Time Machine backup - it's not there on my current system.

My main question is: does the absence of com.apple.mio.VDCAssistant.plist indicate a deeper problem that ought to be fixed? If not, I can live with not being able to import video directly to iMovie directly from the camera.

If it does indicate a deeper problem, I guess it's time to reinstall the OS. If that's the case, can I restore the system from a time machine backup or will this just reintroduce the original problem?

Thanks for reading - I'd really appreciate any input.

Update

Reinstalled the OS and the 'cmio' file is there. iSight still not recognised. The iSight issue must be a bug confined to older versions of iMovie, even though they're still supported by Mountain Lion. I'll use QuickTime to import the footage.