Jamie:

One of the pro techs who participates here once commented on the variation in quality of the Bosch line as a whole. It seems they make a Grade A, Grade B; Grade C and this applies to what you might purchase from an MB dealer as well. The Bosch stuff that Auto Zone carries is in my mind, Grade C.

They're hard to find, but it's my impression from searching here, that Beru makes much better plug wires than Bosch.