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I would suspect based on experience that PCV by itself might not be a problem as long as there is no recirculation of EGR. My 1976 280Z came factory without an EGR valve (only 75-76 Federal versions). It had a sight stain in the intake manifold from the PCV fumes but no accumulation of "grunge" that accompanied those later engines where PCV and EGR were mixed. When mixed the grunge was substantial with accumulations from the EGR ports to and including the intake valve stems.
It was one of the reasons why I liked the 1976 model above all the others. It had no catalyst as well as no EGR, the fuel injection solved the emissions problems during that short period of 2 years (Federal version only, Cal had a cat). With the later .75 OD 5 speed tranny and flat top pistons that brought compression readings from 160 PSI to almost 200PSI with the factory 3.54 rear axle.
Maybe the fuel injectors spraying onto the intake valves kept that area clean versus DI that would not. Maybe synthetic oil would help alleviate the situation which must be oil cooking on the intake valve head and stem, but that old 76 Z intake was lacking of any residue anywhere, while the next year (1977) had grunge all over the intake tracts when it got some miles on the car.
regards
Mech
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