Contact cleaners - a moving target.
When my wife and I were working in Saudi Arabia, I purchased Cramolin Red in the electronics souks for SR10 (about US$3) per 300ml pressurized can. In Saudi, nothing can be sold without complete disclosure on the labels (Caig products are not sold there). So each can had on it: Hydrocarbon and hydrocarbon propellants: 95%. Oleic Acid: 5%.
Oleic Acid has been used in the clockmakers profession for over 100 years. Oleic Acid is a derivative of cheap olive oil, for the most part, and can be purchased in food-grade quality (purest) over the counter, and sent through the mails. I mix it in 1/2 ounce quantities in eyedropper bottles using pure naptha as the medium at slightly less than 5%. Why? Contact cleaners such as DeOxit have the virtue (vice) of continuing to react until all the active ingredients have been consumed. So, it MUST be rinsed off after the work is done to prevent further reaction.
As proof-of-concept, find an old actually-copper penny and put it in very cheap olive-oil for a bit.
Once upon a time, Caig was the US distributor of Cramolin products - that ended very badly with considerable ugliness on both sides. To this day, I will not purchase Caig products.
Peter Wieck Melrose Park, PA