On my printer, the teflon tube sticking out of the nozzle was not perfectly aligned with the extruder gear. This caused the filament to be offset slightly to one side and slide on the PLA part that acts as the extruder assembly. After a few hours of printing, the PLA ground down and the extruder started to loose grip of the filament. I now have 2cm of bowden tube inserted into the top of the PLA part on the extruder to mitigate any misalignment.
I think it would be nice, if the printer came with a small bushing installed in the top part of the PLA component, to make sure that nobody else has such problems, the bushing would not be as soft as PLA and would not grind down. It would act as a tolerance buffer for nozzle - extruder misalignment.