How to create dielectric oxidation between steel and brass part?

Q. Gentlemen:

I am a mechanical engineer working on a project where I have two metals (steel and brass) in contact with each other in a small, pinpoint spot that is inaccessible. I would like to electrically insulate them from each other at that point and there is no practical way to insert any type of dielectric in this application.

I'm looking for a way to chemically oxidize or corrode one or both of the metals, so that an insulating layer is formed between them and electricity cannot conduct across the junction. I don't need a high dielectric strength: I'm only insulating electronic-type voltage (5 volts DC). It is a very small contact spot (think of two spheres touching one another).

Is there a chemical, or electrochemical way to accomplish this?

Thanks for your replies.

Don