At least in Austria and Germany plenty of rewirable plugs failed back in the old days because manufacturers dipped the ends of the stranded wires in solder before clamping them under a terminal screw. The solder moves under the pressure of the screw and the termination then overheats. I'd say that was clearly the issue in roughly 90% of the failed plugs I've seen. Unless I've forgotten a few I've only ever come across one failed moulded plug and that was on an early-2000s dishwasher and the plug failed in 2016, taking the socket with it. The socket was only three years old, decent-quality and tested after installation so I'd rule that out.
