The speed change mechanism relies on a clutch that locks a ring gear. The teeth of the plastic part that locks the ring gear had worn away.
Replacement part modeled in FreeCAD 0.21.2
Printing:
Printed on a Prusa XL with 0.4mm nozzle
Filament: Prusament PETG-CF
0.15mm layer height
4 perimeters
supports only on build plate
It fit perfectly, without postprocessing, except for support removal.
I lubricated the sliding parts with a bit of vaseline.
The original part is made from PA66-GF33. Quite possibly the PETG won't hold up to the thermal/mechanical/chemical stresses in the long run. Printing from a fiber-reinforced polyamide might be a better option.
If the PETG part breaks, I'll post an update here.
Let me know how it works for you.
The author marked this model as their own original creation.