Country Boy;) the only function of the glowplug in a Diesel engine is to heat the AIR in the inlet manifold - not the fuel before it is injected into the combustion chamber in the last few millimetres of the compression stroke . The air is heated instantly to around 600 centigrade ( the flash point of diesel) to assist the combustion on initial startup.
The picture above shows the glow plugs wear out due to the reason of running them a lot or trying to start a vehicle with not fuel.
Also glow plugs wear out due to the burn out of the inner heater core due to excess current flow. Check wiring Harness & glow plug timer.
German might be a issue try american:D