2 key points:
1) Use Oil and Water mixed
2) Use a toothbrush to get into the details.
The toothbrush helps with the texture areas on the Milanos, and the text areas on Pharaoh’s. It helps you wash off any residue in those recessed parts, plus get oil in there.
The water acts as a “vehicle” for the oil, and also helps you not elevate oil. The chips don’t need to be bathed in oil. They just need to be dipped and scrubbed in water that has a good amount of oil in it, then wiped down.
I have never even done the “cleaning” step with any soap. I have always just skipped right to the oil and water, and always got great results.
Your chips won’t keep that really shiny look, but most people wouldn’t want them to anyway, or they just look plastic. You probably want them to look a little textured like clay, but with bright colors. They will definitely stay nicer than they were when you got them, so it’s not wasted effort.