The extruder has the greatest potential for improvement. Between filamentdrive and hotend there is a thermal insulation made of teflon. The filament is heated in a fairly large and undefined area depending on temperature and feeding speed. In addition, the volume of the hole in the teflon cylinder increases with pressure and with temperature. Both factors mean that in slic3r the retrack must be set to a few millimeters. Nevertheless flow of filament does not stop. It's not possible to produce multiple parts in one operation without blobs and threads.
Replacing the filament is also a problem. Sometimes it works, sometime it sticks in the extruder so the extruder must be taken apart.
I shortened the original teflon cylinder and replaced it by an actively cooled aluminum heatsink. The area with the largest temperature gradient is now reduced to a few millimeters. The retrack can be reduced to 1 mm in slic3r to interrupt the flow of filament. Also replacement of filament is now easy to do by turning left the big gearwheel (while the extruder is still heated) until the filament can be pulled out by hand.
Allways use dry filament, bake if necessary or dry with silicagel in a closed container.
Manufacturing data in download section