This film--i am thinking probably shown in movie theaters before the main attraction--is from c. 1966, showing el maestro lapping Monza in his 1951 Alfetta 159. Some wonderful sounds and footage. Gotta love his shiny leather driving shoes when he steps out of the monoposto at the end!
In the early 70s, a fantastic documentary was made about the life and career of Argentinian maestro Juan Manuel Fangio. I was fortunate enough to have a father who owned this movie on VHS, and I watched as a kid until the tape got worn out. While trolling through youtube, I discovered that someone had uploaded two of the movie's best scenes (sorry this version is in Spanish, but at least you can hear his actual voice).
In the first clip, Fangio, now retired, is reunited with his 1956 Lancia-Ferrari D50 at Monaco, and drives it flat out with some incredible onboard camera work and stellar editing. I get chills every time I watch this clip, and I have always loved the theme song that comes in at the end during the slow motion sequences.
In the second clip, Fangio tears around a deserted Monza circuit at sunset in his beloved 1951 Alfetta 159, in one of the most atmospheric parts of the movie.