Photo of the situation could be helpful. I have the same motor but I'm betting I can't see the bolt to compare without taking things apart.

The go-to method to extract a smaller bolt like this when you can't get a bolt extraction socket on it is to cut a slot and use Impact but of course caution is in order because you will weaken the head.

That said if you cut or break the head off you can remove bthe part and have lot of fresh bolt to attack with penetrant and vice grips.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)