grimey residue in oil filler neck
 

hey all,

i was doing an oil change and noticed that looking into/down the oil filler neck, there's this grimey residue that i really can't identify. a buddy of mine stopped by just to see what was going on and he said that it might be caused from condensation from somewhere. any thoughts? important to keep an eye on?

it doesn't seem to be going all the way down but i didn't have a flashlight to really inspect it.

thanks.