Sue, I've never heard of an African Grey that doesn't talk. That is to whacky.
Read an article in Discover about African Greys a few years ago that focussed on the fact that the researchers were actually teaching the Greys to talk, not just mimic, but teaching the meanings of the words. The oldest one actually made sentences. He would help train the younger one. One day the younger one was fooling around and making mistakes and the older one looked at him and said something like, "Get it right, will you." And he used to tell the researchers not to do anything he wouldn't do, and to have a nice evening. It was truly fascinating.
And now I hear about one that won't talk. Takes all kinds, I guess.