Mercedes-knowlegable mechanics are rare birds in WV. The only place I can recommend is Astorg, the dealer in Parkersburg. They are right at the 100 mile limit, but are a truly first rate operation, and their labor rate is (or was, a couple years ago) only $55/hour. There's bound to be a few good shops in Pittsburgh, you might have better luck starting your search there.

HTH,
Tom
in St Louis, late of West Virginia