I id a few black squirrels with neatsfoot oil years ago. They turned out beautifully soft and white. I found the key was to keep them VERY stretched, almost to the point of breaking. I also worked them past the point where they felt dry to the touch. After a few unsuccessful braintan attempts, I feel the stretching while drying is vital. And they have to be dry when you are done.
It wouldn't hurt to redress, just rebreak them again also.
Kyle
Oh, I'd rather use eggs or oil. Cooking brains turns my stomach.