Marvin's policy is easy to understand and follow-trust, but verify because where there are humans involved, mistakes will happen. Just because a part is new doesn't mean it is free of defects. Marvin inspects and blueprints every part. Blocks are completely stripped down including Welsh and oil galley plugs. Marvin has unearthed lots of machining trash and iron particles from every single casting he's ever worked. Here, he finds stray iron from factory machine work hidden behind the Welsh (freeze) plugs. Iron particles like this can plug smaller cooling passages and create hot spots, which raise hell in the water pump and restrict radiator cooling tubes.