Gray green substance under oil cap - Cummins ISX15

[SupVit]

Hello.
2015 Prostar with Cummins ISX15 2350. 370k miles. I'm the owner since 197k.
I decided to change the oil, warmed up the engine to 140F, opened the cap and found a dark gray-green oily substance. On the cap and about 2 inches into the yellow filler pipe. Also, air comes out little bit from the filler pipe. It can be seen under the light of a flashlight, like in one video on youtube channel where Rawze checked for the green Prostar. I don't know how much air should come out, I have never opened the cap of a warm engine.
I opened the breather filter too (I need to change it, although it does not look dirty, I changed it 130k ago). The oil on the filter is not dirty. The plastic under the filter has small amount of oil in which there are beige drops. Around the cover there is also a gray-green substance. The cap of the coolant is clean. Level does not change. For 2 years of owning a truck, I have never added any coolant or oil between replacements (12-17k).
What is it? Looks like coolant in oil. But substance is dark gray instead of milky. Where should I start looking for a problem? I think the problem appeared recently, because 13k ago I changed the oil and the cap was clean.
Thank you.

[Waterloo]

Is this the first time you are changing the oil? I saw you have... Looks like moisture to me, and purchase the forever crankcase filter from Cummins...

[SupVit]

No, I do all regular maintenance and fix most regular problems (that don't need heavy specific tools) by myself.
What do you mean saying Moisture? Air moisture outside (weather)?
Or some changes in engine operation caused an increase in humidity inside and these gray deposits?
Sorry, my English level doesn't let me understand even main idea sometimes.

[Waterloo]

Like I stated, looks like moisture build up to me, unless you are seeing something that tells you different. You can do an oil test to see if any coolant is in the oil, but odds are, if the truck is not driven regularly, it is moisture build up. This is common in winter.

[SupVit]

For 2 last weeks I always worked near snow storm in PA, MD, NY and also in Tampa, FL having horrible humidity. Perhabs this is the problem... Thanks
I'm going to change oil now, already brought plastic bottle for sample. And I will check for oil cap later.

[SupVit]

I got oil test result. Looks good. Hope this gray stuff won't appear anymore. Thanks.
----
VITALII: Steady does it for your Prostar. These wear levels are almost identical to what showed up last time, and steady wear like this is how a healthy engine should look in analysis. Of course, this was a shorter run so less metal would've been nice, but these numbers aren't out of line after 13,000 miles of oil use. Iron is still well below average on a per-mile basis, and other metals look great too. The viscosity is in the 15W/40 range, as expected, and no contamination is present. Low insolubles show good oil filtration. All is well for your ISX at 370,000 miles. Keep it up!
---

[Aleeex]

I had something similar happen in Minnesota during the winter. I wasn’t using a grill mask. The oil wasn’t getting hot enough to evaporate the moisture


After the mask, never saw it again

[tree98]

See, masks do work :)

[SquareOne]

^^lmao