Badinfo, with the belt off have the "tech" check that all the accessory (alternator, A/C compressor, power steering pump, air pump, idler, fan, water pump) pulleys turn easily ... one or more are likely seized which results in a new belt quickly self-destructing. Although if something is seized the belt would likely screech too ... hard to imagine a tech failing to hear that. Also, have the tech check that all the pulleys are aligned properly and that the damaged pulley grooves are near-perfect ... otherwise replace that pulley. Another possibility is that the belt tensioner is shot. Is the tech MB-trained or one that works on any type automobile? Best to have a knowledgeable tech work on your MB automobile.

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Fred Hoelzle