Gosh, gotta love that cast iron. I know most of my friends think I'm nuts, but I looooove my cast iron. Most of mine are old, too, from my parents, but probably not that old. In one the seasoning got messed up somehow, it came to me that way, and it's taken me a long time to get it just right. Of course, I didn't burn it in a big fire.
I agree, clean it up with just hot water, oil it and put it in the oven. It will be plenty sterilized.
PS I hate house mice. They are find out in the fields where they belong, but when they come it the house. It's on, brotha!