While I was working in the engine compartment I had a look around to check the general condition of things. A look at radiator showed this. I have been chasing an oil mist issue and it looks like the mist and dust combined to coat the fins with a black gunk. What a surprise huh. This is an aluminum radiator.
Dooder had a similar problem with his car - his oil was coming from his front crank seal, and being picked up by the fan and like yours combined with dirt from the air it was probably 75% blocked!
He also blew his motor by running out of oil, so keep an eye on it.