Quick Disconnects (QD's) have caused many problems in the past. Fuel QD’s from the main fuel filter to the fuel control have failed at the break-away causing the valve to shutoff. The QD on the engine deck, where the line that comes from the fuel control governor ( the forward blue one ) down to the fuel tank, returning fuel fails and the governor cannot function properly.
The QD’s in the oil system fail and causes some major problems. If the lower one coming out of the tank to the engine fails there is NO oil to the engine. If the upper QC ( breather ) from the gearbox to the tank fails, pressure in the gearbox increases causing the starter seal to leak and erroneous torque readings. The torque is sensed by balancing gearbox air pressure against torque oil pressure. I have run across the problem just recently.
This problem can also be caused by the line getting kinked or failing internally and shutting off the air flow. The QD on the oil line coming out the left front of the engine to the deck ( the silver one in the photo ) is taking the hot scavenge oil down to the thermal valve then to the cooler then back to the tank.
I know of cases when that QD fails the oil can’t leave the engine, it gets very hot very quickly and the engine is junk. Depending on your situation, STC’d or Public use, gives you direction on what you can do. If you can’t get rid of them be sure to inspect them regularly. If possible replace them with straight or bulkhead fittings.