Xf , excuse me resurrecting an old thread but as part of my spending hours researching the m112 engine ticking, of everything I’ve read your 2015 thread which I’ve just come across way down the search list is definitely the most succinct and articulating where my own thoughts had gotten to. Was almost a relief to hear someone else articulate - what surprised me though was the lack of take up from a response perspective. Is a consistent thread on Mercedes forums and chat but less so on Crossfire.
My thoughts were are your list above, with one other possibility of exhaust manifold leak. I can’t believe that your thread starter didn’t start an avalanche. Did you ever find out/get there. I’ll happily exchange my thoughts ad nauseam as I continue to persevere.