So, p520 foam filter comes with the notoil stuff from the factory.
That goo and oil do not mix.
If you switch to oil make sure it is cleaned first (highly recommend switching to a p500 filter).
But the amount of liquid you are showing is more than "I added a little oil to the filter".
And if it was from the crankcase the dip stick would be dry.
So now I want to know what is it, 80% water mixed with p520 filter goo?
I'm running an aftermarket foam Uni filter with filter goo. I think I saturated it with filter goo the last time I cleaned it. I just cleaned it again and went sparingly on the goo. Is the p500 filter different than the 520? I can't remember if the Uni Filter I bought was spec'd for a 500 and/or a 520. I assumed there was some water mixed in, but I don't see much separation in the jar, and it's pretty oily to the touch.
Just checked the level again.
With dipstick screwed in:
Not screwed in (IIRC, this is how it should be checked, correct?):
So it does appear to be low. Best guess still is that it got sucked up and out of the crankcase vent. Somehow.