Frayed, Stuck, Cracked
The pilot reported an unusual amount of oil was being consumed and oil pressure was fluctuating. There were no external signs of an oil leak. When bleed air was turned on, a fine mist of oil issued from the heater vents. Troubleshooting found the engine vent line (p/n: S51-14) had collapsed, internally pressurizing the case and causing the oil to leak internally into the compressor.