Earlier quoted context omitted.
I did this for a year and a half in high school. The McD procedure involves draining the barrel, flushing it with water, then disassembling each barrel assembly and removing every o-ring and gasket. https://youtu.be/SaYTx7qNJU4?si=Y2ZjWHQJHiKQfAFh Each part is washed in detergent, rinsed, and sanitized. Rings and gaskets are relubricated with food safe petroleum jelly, then everything is reassembled. Forget one ring…
Basically right, where I worked the parts were set in trays to air-dry overnight. There was a spot on the tray for each part, o-ring, and gasket so you could easily see if any were missing. The machines were reassembled the next morning. So the closers only had to break them down, wash, and sanitize. Once a week any dairy mix left in the machine was discarded, this "breaks the cycle" of any bacteria in the mix. So on…
I'm guessing 24/7 operation changed when and how the cleaning was done, leading to more contamination instead of less.