The "caustic" cleraners have little in them that has not been recommended as a component of coolant...... which has long been suggested to have some strong base content in it (like lye) to inhibit corrosion of iron and steel.
if you are GOING TO disassemble for some good reason, purple or it's relatives are a really good item to use on PIECES. I would NOT advise spraying them over an assembled machine, you don't know where they go.
I'm pretty sure that's Forrest's point.
Most alternatives, like solvents, kerosine, stoddard, etc are flammable, which water-based cleaners are not. That can be an issue.
But the stuff got ON the machine via petroleum-based stuff, so it may be able to be removed by the same type, with less problem than if you introduce water-based things.
My experience is that even good-appearing machines that work harbor unseen botched repairs, "bubba" fixes, etc. So for anything which is doubtful, I may take apart enough to verify condition. But, as noted, you can get in trouble that way, and if you want to make money, clean it up and use it until matters are such that it becomes obvious repair work is *required*, not just nice.
As for scotch-brite, yes, you can, but closed coat fine sandpaper and oil will do anything scotchbrite will do, and drop less grit. You can work for days with either one and not take off enough material to measure.