Just based on my own experience, might as well open it up and take a good hard look at the work you did on the valve seals. You don't have to take the cover all the way off (over the eccentric sensor) to look at #2.

Or, if you can do a leak down and compression test on number 2... Wasn't till I did a compression, leak down and smoke test on mine (Cylinder 1, after much part swapping) that I was able to rule out the rings, many other parts, vaccuum leak, etc and focus on the exhaust valves. Then after much careful inspection, realized one of those wasn't done properly.

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2007 X5 4.8i - 12/06 Build - Silver/Black - 3rd Row