Burnt out glow plug rods are often the result of malfunctioning injectors. These violations cannot be attributed to a defect in the glow plug.
If such glow plugs -arrow- are found, it is not sufficient to replace them. The functioning of the nozzles should be checked for their jet, chatter, pressure and tightness (service station work),
In this case, you should pay attention to the fact that with short, fast cycles (4-6 cycles per second) there was good spraying and cutting off the jet.