I've seen it on 6.2's over the past five or six years. Each one has turned out to be the result of a bad fuel injector. Running too lean in that cylinder. The discoloration of the valve in that cylinder gives it away. When you put it back together again, I would replace all the injectors.
It's the one main reason why I always check the long-term fuel trims on the Tech 2 at every oil change on my wife's Escalade. Paid off, around 177,000 miles I noticed the long-term fuel trim on one bank was 16%, while the other one was 3%. New injectors brought both to less than 2%.