[Gumpy]

Yep - that what you need to do. Replace the tensioner and check to make sure the guide rails are still in good shape.

 

[Gumpy]

2008 should be out of the range of weak balance shaft sprockets but if you find the sprocket worn, it’s an engine out job to replace the sprocket. Do you have a borescope to check the balance shaft sprocket and guide rails?
For kicks, try a new tensioner before tearing into the timing chain.

Sixto
05 E320 wagon 201K miles

As Maxbumpo pointed out, a good fiber optic borescope will tell you of there are any balance sprocket issues or if the guide rails are seriously worn. Replaceing the guide rails or balance shaft sprocket is a very expensive trip (~$10k) that requires pulling the engine. Just got done replacing the phasors and pulse wheels on my 2007 E350 and the sprocket was in perfect shape and the guide rails hardly worn at 130K.

 

[Gumpy]

Here's part 2.

GREAT VIDEO! Note that you need to remove the alternator in order to get to the tensioner. The tensioner can be reused (they seldom fail) and there is another video that shows you how to reset the tensioner. After installation, you also need to release the tensioner by holding the crankshaft stationary and applying force in a counter rotation direction in order to release the tensioner - another video.
Remember that the center valves on the exhaust cams are left hand threads and on the inake, right hand threads. Grease the back of the pulse wheels and be cautious that they do not rotate as you torque down the center valves. New pulse wheels cost about $10 each for genuine MB. The pin on the back of the wheel often gets damaged during removal - install new ones.
WARNING: The phasors (camshaft adjusters) have three reference marks (pin pricks or etched). Two need to be alighned with the housing edges as shown and the third needs to be pointing up in reference to the block. This applies to all four phasors. The video does not show this, but if the logos do not line up with the holes as shown in the video - DO NOT START THE ENGINE.