DH's grandmother cured DD's cradle cap in a few hours. And it was BAD. Her hair was falling out in chunks because of her cradle cap.
We just rubbed some vaseline on it, left it for half an hour. And then washed her hair (well, head... lol), rubbing it gently with a wash cloth and it was nearly all gone.
We repeated it the next morning and her head was soft, smooth, without a sign of cradle cap. She's never gotten it again.