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Something seems wrong. Yes Mercedes can be expensive at times but this does not make sense. I see the part available for less than $2 from any Mercedes dealer.https://www.mbdirectparts.com/oem-parts/mercedes-benz-engine-timing-chain-tensioner-005401305000
Sorry about all of the fuss. Never saw the ball when I removed the tensioner unit and figured that it was never there when I started to reinstall it.