Gray green substance under oil cap - Cummins ISX15

[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!
---