Discontinued by VW many years ago, and no longer available.
These units were prone to cracking at cylinder four, due to design issues.
Cast iron can be welded but, only by skilled persons that know how to do it correctly. Otherwise it will simply crack again adjacent to the weld.
A hole must first be drilled at each end of the crack, to prevent further stress. The crack itself must be ground out to both widen and expose bare metal in the entire crack area. A special material welding rod has to be used to fill and repair the area. This should only be accomplished by a very skilled casting welder.