Just to reinterate...I consider myself a pretty
good cleaner, not fantastic, but decent, and I would not touch it. The slight
patina looks incredibly thin and any attempt to "even it out" would probably end up showing bare metal. At best I would soak it in distilled water for a week or so and brush it with a soft nylon brush to see if anything moves (some of the lighter colored stuff on the
obverse may leave). If anything is removed, I would continue until nothing more leaves the coin...but I doubt that would do anything, really.
Chris