I've never seen an M112 manifold fail like this, I think you could have found a good used one for $50. Did you really pay $1200 for a replacement manifold? You can buy a complete M112 junkyard engine for $400-$600 these days...

__________________
98 Dodge-Cummins pickup (137K)
13 GLK250 (157k)
06 E320CDI (341K)
16 C300 (89K)
82 300GD Gelaendewagen (54K)