There is the rub - #O-C1-01
Part #23401-O-C1-01 has the third tooth partially sheared at the tip and the fourth is nicked.
This will mean that the pivot is suppose to stop the gear from moving may skip the first and second and third tooth. Normally the toggle will skip the first and locked from reverse at the second tooth. Also, the first and second are worn. I would say this is a perfect example of not wrenching the advance lever when something is stuck.