That does not sound too complicated. Perhaps I'll have a look tomorrow. If the culprit is that simple, I'll be pretty happy. Could the spacer you mentioned, or any other part, dislodge or otherwise move in a manner that causes damage? Also, how does a hydraulic compensator collapse?

Having never taken the valve cover off on my own, and not being familiar with what's underneath, I am a bit apprehensive. Still, I get the impression that there is nothing delicate or easily breakable under there.

I am also now wondering if this problem could be the root of my occasionally rough idle, which is now considerably more pronounced and continuous.

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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black