I would also be interested to learn how to bring back the alloy parts under the hood back to their original luster. My '95 C4 is rather spotless otherwise, inside and out, except for the parts that are some sort of alloy in the engine bay. I have tried several products, and even a gentle rub with 00 Steel Wool, with no result. Most suggestions I have seen that really work (YouTube) require cleaning the parts off the engine, which is not an option for me.
Hopefully over the next few days, someone will come up with workable suggestions.