www.jackbenny.org

The Archive of American television has been compiling interviews with TV personalties for years and adding them to their web site:

http://emmytvlegends.org/

These interviews are very lengthy and provide an oral history of television. They feature very prominent people like Walter Cronkite, Dick Van Dyke and Ernest Borgnine, but also have many secondary or behind the scenes folks as well. Some have links to the Jack Benny Show. For example, Irving Fein was interviewed for over two and a half hours in 1998. Here's the link to his interview:

http://emmytvlegends.org/interviews/people/irving-fein

Fred De Cordova is also featured in a long interview. There is discussion about the time he spent directing Jack's TV show, but most of his time is spent talking about his years on the Tonight show.
This project started after the Benny cast as well as most of the golden age of TV had passed away, which is too bad. Much or what is here is preserving memories of junk like Judge Judy, but that's what's on TV now. Nonetheless, there's still something of interest here even for those who think TV peaked in 1965 (with the exception of Frasier).

There is also a very long (two hour) interview with George Balzer on the TV Legends site that I mentioned. Unfortunately , despite the time spent, the interviewer got very little out of George. I don't know if it was because of advanced age (George was around 86 at the time), or the fact that he just didn't want to share much (maybe both). I was pretty psyched when I found this interview, but as I watched it I grew more and more frustrated by the responses. I ended up skipping forward several times, so I haven't heard the whole thing. But I did sit through the bulk of it, and all I got was that George really didn't seem to care for Irving Fein or Red Skelton, and he really, really liked Jack. No big revelation there. Who didn't like Jack? So anyway, it's out there, but you've been warned.