Cummins 8.3 ISC Dripping Oil out Breather

I've got a cummins isc in a 2013 Freightliner M2

Recently started getting oil drips on the floor. Upon inspection, they seem to be coming out of the oil separator tube. I changed the crankcase breather filter only a couple of hundred hours ago. Could I need another filter already?
If I pull the oil cap on the valve cover with the engine running there is very little blowby coming out the hole.
Suggestions?

 

Do you mean pull the crankcase vent filter and check for clear passages, or the oil separator?

 

I pulled the breather filter. All passages were clear.
Pulled the oil separator. Didn't find any restrictions.
I blew down the little drain tube off the bottom of the oil separator. It was clear. Where does this tube go? I can't see down behind the engine.
There's another little black tube that comes back up beside it and goes into the valve cover. Blew thru it and it was clear as well (where does this tube come from?)

So....I'm still at a loss as to why oil is coming out of the breather tube. Still confused as to how the system is supposed to work....I thought a positive crankcase vent had no atmospheric vent.

 

I can rev the engine to 1000rpm and pull the oil fill cap and can detect hardly any blowby....

 

Dipstick was right at full mark. I drained a liter or so of oil out and the leak seems to have stopped. Note to self, only add 18l of oil next change I guess.