By failed I mean "got hot enough to smoulder and turn a crispy dark brown" or even "hot enough to burn holes around the pins". If you look at a white plug and see a brown circle around one pin you know what's going on. I've hardly ever seen that with stranded wires straight under screws (technically illegal according to German VDE regs) so I'm fairly certain the solder was the issue. It's similar to the troubles with household-size Al wiring in screw terminals.
Rewirable plugs and trailing sockets have pretty much become a DIY item here, everything sold in a store will have a moulded plug on it. Of course electricians do use them for repairs and site-made extension leads too but in Germany the general assumption seems to be that repairs are supposed to be made with OEM parts (i.e. if a moulded plug fails or the flex is damaged near the plug you need to replace it with an entire new flex with moulded plug supplied as a manufacturer spare) and site-made extension leads require all sorts of compliance paperwork and testing so it's safest not to touch anything. At least I see that attitude becoming more and more common in web forums.
