There are several brands of dielectric grease that you can use to keep the brass from corroding. I use LPS #1 or 2 sprayed on lightly to keep most of my electrical components that are exposed to the elements from corrosion. You can also use anti-corrosion grease, sold in tubes at most auto supply stores. Just apply a thin coat with a Q-tip. If the tool is exposed to extreme weather such as marine you might want to have the contacts gold plated or at least silver cadded.