Ended up not needing this. Brand new still in the Mercedes bag. This the check valve between the vacuum pump on the main vacuum line. I think this is only for 1980 to 1985 OM617 cars.

List price from MB is $87. Selling this for $70 Shipped USA.

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'80 300SD - '83 240D - '00 E55 AMG - '02 G500