White gunk on my keys?

Hey guys, I recently acquired a Royal Quiet De Luxe from my grandparents and after several decades in their attic it came out with this white gunk all over its keys and only the keys. I've tried scraping lots of it off with a coin and wet toothbrush but it's still got a lot of visible and residual elements of the gunk left. It's white, gross and mildly pungent. How should I go about removing it and what is it?