The scenes where they identify the square peg/round hole problem and where John Aaron and Ken Mattingly get the power draw down are some of my favorite in any movie. Must watch for any engineer
They achieved the important function ("flow cabin air through the filter") in a totally different way.
https://www.nasa.gov/history/afj/ap13fj/15day4-mailbox.html
https://spacecenter.org/apollo-13-infographic-how-did-they-m...