What would cause the arm on the rooster comb/detent lever to pop out of place ( see picture ). This is the third time this has happened , get "REALLY TIRED " of dropping the pan .

It it missing the washer and "E" clip on the throttle pressure lever? That would allow the rooster to move out of alignment with the detent ball. It may also be bent. With the shift linkage removed to should not overrun the low 1st position. I think the shift valve plate hits the rooster to keep it from going too far.