Cleaning Silver Engine finish

[Deye76]

While the cases are apart for re-build, I was at machinist (also happens to custom paint) friends place to press in new bearing race, and happened on a can of Dupli-Color Specialty Reducer (Autozone), poured some on a rag and went after the bottom of the case. Stuff works very well. I don't think one should pour direct and let soak, may lift the PC?