The DVD Times website has a mostly positive review of the DVD release of "Koko: A Talking Gorilla".
This 1978 16mm film is grainy in quality and follows the story of Koko, a mountain gorilla born in San Francisco Zoo in 1971. Koko was taken to Stanford University for an experiment in which Dr Penny Patterson taught Koko the basics of American Sign Language.
I vaguely recall seeing this film many many years ago. It'll be interesting to check it out again.