Applying a light coating of oil or protective fluid over finished zinc-plated parts is a common practice to enhance corrosion resistance, but it may not always be necessary, depending on the environment the part will be exposed to. If your zinc-plated part is exposed to a controlled, low-humidity environment, it may not need an additional coating. But if it will be exposed to high humidity, water, or corrosive elements, applying a light protective coating is advisable.