Have you tried to put a magnet on the filings to see if it is Ally or steel ? if it is ally I would say its you're sump threads that have striped due to over tightening the sump plug, it happens over time and gradually gets worse until there is no thread left, it happened to mine but I managed to tap the sump out to a larger size while still on the car and I then fitted a femco oil drain plug which makes oil changes easier now.