i dont know if this is possible or not but on several crt monitors that i have had i was able to degauss it? i dont know what that is but if i was having problems with the monitor it always made things look clearer etc. well that was aftera few seconds as at first it makes a funny noise then the screen wobbles around.
i dont know if any of this is possible on hte crt imacs but that is my idea. otherwise i would say that it looks like hte crt tube could be going.