Correct, the black box is an oil separator or collection device that allows for oil vapor condensation and flow of oil back into the oil sump. The excess vapors are routed up to the intake and burned.

The problem with the PCV 'system' is oil condensing in the vacuum lines, solidifying, and eventually blocking the vacuum port to the intake manifold. When that happens, the crankcase pressure builds and seals start to pop under the pressure. The weakest seals are the cam seals, front and rear, followed by the RMS.

On my current project car with 178K miles, the small vacuum line from the PTC nipple to the intake manifold was plugged, as was the small nipple on the PTC valve (which isn't really a valve). Oil was leaking, weeping, past the rear cam seals, which now needs to be fixed. There is a possibility that the RMS was also compromised, we shall see.

Placing a latex glove over the oil filler hole and starting a warm engine is the best way to determine of the crankcase has positive or negative pressure.

Using synthetic engine oil reduces the risk of sludge buildup.
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My back feels better when I sit in a Volvo seat