trimmer bump knob problem
I have a Homelite string trimmer (TrimLite model UT20760). The bump knob (officially called the "spool retainer") is stuck to the spool so I can no longer screw it off the drive shaft separately as designed. It is stuck so hard that tools (vice, vicegrip) are of no help trying to separate the knob from the spool. No cross-threading is involved (I can screw the bump knob/spool on and off the drive shaft as a unit and replace the line that way).
This is the second bump knob and spool that have seized up together in the past year. Does anyone know what might cause this and how I can prevent it in the future?
p.s. the shaft itself is not heating up