climberman,

Good move on taking the PCV out of the loop. The scenario you describe is typically a valve guide problem. You state the rebuild included head work. I wonder if the shop that did this checked the wear on the guides, replaced the guides or knurled the guides. I won't cast dispersions, but a good automotive machine shop would have surely addressed this during a head rebuild.

I don't know what a 250 uses for valve stem seals but this would be an area to keep in mind too. Talk to the machine shop.

Stuart