it is this one ? :
To full fill the crack you can use some sculptey, and you hard it with a hairdry (i used this method before and it works well.)
But some other members of the forum may have more interesting method.
To paint it, you'll need to use some White Skull from GWS paints. The photo shows i saw shows the coat as really white (a clear perfect white). (If the coat is a bit grey a cream, you'll need to combine the white with another color (some vermin brown (really few) for the cream or some grey codex for the grey.)