Is that the aluminum "head bolt" sealing the timing section of the head?
I thought this was an issue on early 06 n52 models... Can you confirm that all four bolts are there? There's one by the OFHG and 3 more below vanos sprockets. I paid a shop to drill them out and replace them after I found all four sheared off during valve cover job. I'm definitely one of a very few people who fixed this, it's probably fine to leave them as is.
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