We have the same switches on the makita grinders work supply. Mines been away for repair under warranty twice in 9 months. First time it came back, it lasted about 5 on/off cycles and fell off.
in this diagram the part numbered 53 slides between the field coils 1 and the housing 50 and can clog with grinding dust or the grease can go stiff
this is a plastic rod that actuates the electrical switch 43