BMI A320 mag plugs with missing oil seals (leading to total oil loss on both engines.) Both of these incidents feature heavily in human factors courses, and have lead to changes in practices that are designed to prevent re-occurrence.
You have to wonder some times how you can manage to prevent re-occurrences.
On May 5, 1983, Eastern Air Lines Flight 855, a L-1011 registration N334EA, while flying from Miami to Nassau, shut down the #2 engine due to low oil pressure and began a return to Miami. Both of the remaining engines later failed. Without power, flight 855 descended from 13,000 to 4,000 feet (1,200 m) before the #2 engine was restarted and the aircraft landed in Miami without injuries. Incorrect engine maintenance had led to the loss of oil on all 3 engines. (seals not put on the mag plugs)
Lessons get lost and it's why the safety people will never be without a job, and accident investigators unfortunately.