The Delrin extruders are designed to wear out....

However, when it stops extruding and you unload the filament how the end is deformed can tell you a lot. If it is mushroom shaped at the end then something is too hot. if the gear has taken a big chuck out of the filament either the filament ran too long on the gear or the filament is bad (It can happen PLA over time can absorb water from the air). In the case of a spring plunger, the tension is too tight.

Also, if when the fillament extrudes as your loading and it comes out of the nozzle crooked then the filament path (the heat sink/thermocouple/nozzle) has particles in it and should be cleaned out.

Hope this helps some