Andy,

Have you tried ringing the flyback to check for shorted turns? Dick Smith (of capacitor ESR tester fame) has a great little matching flyback tester, available wired & tested, or in kit form. It is available at the following link:

http://www.monitortest.net/

I have one and it works great. Tests in-circuit so you don't have to unsolder the flyback. Cheap, too! Their ESR tester is legendary.