Just an FYI, I remember pulling parts at a Chevy store for various repairs.
It would always irritate me that so many parts were shipped with some Half-A_ _ed paint job over the top of oil or grease on the parts!!
Almost every cast iron part was this way, boxed or not!!
I then had to remove the paint/grease from my hands. It seemed so stupid the way they did it, paint over the grease!!
Now, sheet metal parts were not that way, body parts, etc were sprayed with a primer over cleaned metal.
In the assembly plants the cast iron parts were delivered in the cages, but they were treated the same way, except there was not as much grease to paint over. I believe this is partially why you can see painted and not painted parts like a master cylinder.
Just some random info.