I thought the bushing could also build up accretions in certain areas but I couldn't spot them by eye. Anyway I gave it a try to polish the internal bushing. I removed the center cap of the spool including the spool holding mechanism. Now you have the full diameter of the bushing accessible. I took some cotton buds and cut them in half, put the plastic end into my akku drill and placed some diamond polishing paste on the cotton bud. I worked the whole internal area of the bushing with several buds and paste from 6 micrometer to 1 and that worked a treat! I now have them as free running as I wish them to be and cannot recommend this highly enough to people having the same issues.
So together with polishing the spindle and center grub screw as well as the spool holding latch I think even the worst performing pin can be re-transformed in a 'runner'.
