Hard to tell what you have photo'd Beth. There is evidence of a woody. (Improperly mixed Alloy). Could be a lamination, there is a lot of gunk in the area.
It appears to be a lamination issue to me - relatively common, and doesn't add much, if any, value. But it is an example of an improperly mixed alloy as Pickin' said.
My understanding is that these coins were once perfectly fine, but over the decades the lamination detaches and it end up looking like this.
I would see what happens with a soak in distilled water and a q tip roll. Another way is to stickit under hot running water on a terry cloth. If nothing happens than you can try acetone.
Nothing wrong with leaving it right there. Acetone sometimes cleans more patina from the surfaces. It is really easy to take to much originality from the surfaces. That gunk looks like it is staying, I would just leave it. Water is always the best starting point for restoration. It tells you a lot about the process.
