First I had my oil tested at Blackstone - thankfully with negative results. Potassium or sodium levels in the oil would indicate coolant in the oil.
Second, since I am new to the truck, I didn't know if the "soot" was residual from a prior event or symptoms of a new problem. I drained enough coolant (into a clean bucket to put back in) and removed the coolant bottle which I cleaned with soapy water. I could only get a rag into the first chamber so the other three chambers had soot which I couldn't remove. My goal in doing this is to see if the soot returns (which thankfully it has not).
Third, I put on a Dieselsite coolant filter.
Finally, I checked the oil dipstick for irregularities (which I did not see).
I'll try to post pictures later on.
As an aside, my oil cooler orings were recently replaced. I'm sure others will chime in and suggest that oil - coolant crossover often occurs as a result of deteriorated orings in the oil cooler.
Except for clear condensation, my degas bottle is clean at this time.
Although I forgot to mention it above, I did pressurize my coolant system to 15psi and I didn't see a pressure drop over the 15 +/- minutes that I kept the pressure on. In case it helps, A/Ox4 puts out a YouTube video on how to pressure test the cooling system.
Unless the soot returns, I'm going to assume the soot was from a residual problem. If I were you, I would do the same.
I think the other thing I read about when researching the issue was the potential for cracked injector cups. I believe you can test that by removing the injectors and pressurizing the coolant system. Unless the soot returns, I don't think it's necessary to go there.