I'm surprised a search here didn't bring up any threads, we discuss this movie here every few months. Seems we are divided by the guys who love the movie like you and I and some who find it boring because of the lack of dialog. You say the doc is out on DVD... hmmm I may have to look into picking that up.
In the documentary he says at one point the one of the film cars (908?) was leading the race so they went to the director and told him if they stopped pitting to reload the camera they would win the race.
IIRC The director said the producers would rather he come back with film than a trophy.