This article has a section about replacing mica caps inside audio IF cans, if you're curious about that:
http://antiqueradio.org/Admiral24C15Television.htm
Since you lost both picture and audio, I wouldn't monkey with those cans yet.
It's possible that you have more than one problem:
1. Whatever caused weak audio in the first place. (Maybe your audio just needs alignment, or perhaps the mica caps need replacement.)
2. Whatever led to the loss of both picture and sound.
Before opening up those cans, I would definitely double-check your recent work (#2), since that's when the picture+audio problem arose, and you had a good picture before.
As Dave suggested, it may be wise to try some diagnosis before shotgunning more components. For instance, if you have been using channel 3, you can at least switch your source to channel 4 and compare the results.
Phil Nelson