[John Lawson]

Here’s the solution for 10.8 users. The issue seems to be something to do with the way the new OS handles beamsync AKA V-Sync. You can force the OS to use beamsync on demand with this litte app called quartzsimple:

https://mega.co.nz/#!rMRFyAgI!ILaOu24pLyfob1cFys2S-zuVhEtfPQrllDWW7_qcG2U

Open it up and press CMD-B, then select force beamsync. Now hide the app or minimize it and try playing back your video in FCP7 again. It solved the tearing for me.