Get Perian to work in Lion
Another shot in the dark...but this page suggests downgrading to Perian 1.2.2 on Lion (see "Solution 1"). 


  The latest version 1.2.3 of Perian doesn't work on Mac OS X Lion. So if you have a Mac running Mac OS X 10.7, say, Lion, you have to downgrade the previous version, say 1.2.2. The version of 1.2.3 of Perian does not support QuickTime 10 in Lion and  fails to fix the loss of audio after one second in xvid files with ac3. So if you have a Mac with Lion, converting video to QuickTime is highly recommended.


However, that particular page is all about how to play AVI files with Quicktime, so it may not work, but might be worth a try?