A new belt was installed 1 year ago (previous owner) by a non Mercedes garage (the job done on the water pump didn't give me good impression also...) so I am having some doubt if it was done correctly.

Can this position change in 1 year by itself? I thought it should stay.

Is this position equivalent to trying to overtensioning the belt or trying to do it correctly on a worn tensioner?

If the tensioner is worn and need to be changed: is it recomended to also changed the damper and the tension adjuster also? anything else?

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From 300CE to SLK230K