Originally Posted by cancrusher
the metal shroud on the spark plug wire (the part that goes over the spark plug tip)
This would be the plug connector. MBZ connectors have resistors in them, so it's possible that one of the resistors is working overtime, but more likely that not, you have a defective wire or two. My first question would be "Where in China are they made?"
There should never be a need to replace MBZ original plug wires anyway, unless someone has broken one. They are all copper and usually last forever. Now the connectors are a different story. If there is ever a continuity problem, the connectors are usually the culprit.