[chrs1961815]

You never want to put anything in the oil filler cap as it is vented and allows the engine to breathe. If it is plugged, the pressure will go out the rear main with an oil leak. Another point of interest is to make sure nobody pushed the cap down and bent the tabs.

Do you know what design filler tube is on the car? The later ones are the best, though Ford never quite did get the blowby issue solved.