Here's what I said. Note that I didn't say the others were wrong.
We usually say that someone workson the assembly line.
Prepositions are not easy to learn, or to make rules about. Often, a particular preposition can be possible, but will sound odd or unusual or uncommon.
Thanks for the advice, but could you tell me if the prepositions I included are correct or not? And are you saying that sometimes even when a preposition is used correctly it may sound wrong or strange?