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"The gunk could be from not changing oil regularly! Ford engines ran for years w/o PCV!"
And if you ever tore apart an engine that had only a road draft tube, you'd see why the switch was made. It was not uncommon to have so much sludge in the valve covers that the rocker arms left prints in it. This was the main reason that engines of those days were considered champs if they made it to 100,000 miles.