The misconception is the metal rings (informally referred to as “turbo seals”) are worn, which is true only in rare cases. The more likely cause is an imbalance in the compressor-turbine, leading to gas pressure forcing oil to the low-pressure side. Intake, boost or even exhaust leaks are common causes.
The other main culprit is the oil-return line running back to the engine crank case under gravity. If this line is blocked, oil has nowhere to go and is forced past the metal ring seals. Causes can be a kink in the line; too high oil level in the engine; or excessive blow-by gases in the crank case (or blocked positivepressure crankcase ventilation valve).