I graduated high school in 10976, so a few years before that I went to the movies and saw something…
I tink it was based on a Joseph Conrad story, but certainly not Heart of Darkness. It had a great series of set-up scenes as three or four first-world men see their lives evaporate. (One scene showed a gang robbing a church of its bingo winnings, mistakenly killing the priest, who was the brother of the local mobster.)
All of them end up in a South American hellhole where an oil well is on fire. The only dynamite is deep in the interior, and it is horribly unstable. The men have to pick up the stuff and get it to the oil field.
I thought it was called Sorcerer but could not (last time I looked) find any mention of it.
Let me just note that you remembered incorrectly that it came out before you graduated from high school, when in fact you were a year out of high school at the time. This is actually typical of what happens when someone asks us about a movie that they barely remember. They always get something wrong. Always. That’s why I’ve learned to take everything people say about the movie that they vaguely remember with a grain of salt. If you try to match every detail, you’ll never find the movie they’re talking about.
Sorcerer was considered one of the “can’t miss” movies of that summer - it had Roy Scheider who was as big as he was going to get, William Friedkin who had a string of successes from 1971-onward (French Connection, Exorcist), and an exciting story.
Unfortunately, it was released about a month after Star Wars, which pretty much killed it in the opinion of the director. He went to go see SW at the Mann theater and said it made his film look like “a little piece of shit”.
What bugs me is that a lot of critics were claiming that the name ‘Sorcerer’ is what killed the movie, as folks went expecting more supernatural tales from Friedkin a la the Exorcist. But they seem to forget the movie’s poster (the truck on a very narrow and creaky looking brigde) was more than clear that it was not about anything supernatural.