PLA printing wit PLA extruder

I use a dedicated PLA extruder, inside coated with PTFE tube, and Devil Design PLA. I could print a lot, good results, but after 6-7 month the extruder finish in air printing and the noise of clogged filament can be heard. I recalibrated the nozzle - platform distance and replaced the nozzle with new one. No way. Any advice please?

check/replace the ptfe tube if malformed or pinched

You may also need to remove the cover over the drive gear and clean the junk out of the gear teeth etc.

Thanks, you were right. The PTFE tube was damaged, I don’t know the reason. I shall replace it. Do I have to use glue to fix the PTFE inside the metallic column?

no its normally its only inserted . the length should be the same. after some time the ptfe tube needs to be replaced, so its good to have a spare.

you have to look how it is locked into place. i dont know the up box extruder.
it could be that is inserted from the nozzle side, and the nozzle locks it. or there is a part above the heatbreak that locks it into its place