[Barry_R]

Gunking is very unlikely.

Depending on the atmospheric conditions you are running in you may get some white/gray jelly and moisture condensation on the underside of those unvented valve covers. The covers are the physically highest point in the crankcase, and are exposed to cooler outside temperatures - hence they will be where any condensation forms. Ford and GM moved their ventilation from the intake to the valve covers 45 years ago for a valid reason.

If cosmetics are critical - and I personally see that as a legitimate concern - then you need to have a PCV of some sort just to promote airflow through the engine in an effort to purge vapors. If located in the rear of the intake as commonly done you need to do extra work to prevent oil leakage and consumption - baffles and a liquid containment loop in the vacuum lines will help. But you are now reliant upon just the oil breather cap area for WOT ventilation and that may not be adequate for some engines under high RPM loads.

This is not a new problem - those tall "S" shaped breathers and catch cans all came into being for a reason...