:}:} the missing teeth is your main problem... your best off not even spinning the heli up with that gear like it is.. also on your first pic you posted it sure does look like to me that the main shaft is bent. anyone else see that??? check your spindle shaft too.. put a hand on each of the blade grips and see how much play you have when you wiggle it up and down.. it is really hard to eye a bent shaft.. even a shaft that has a hair line bend in it will cause problems.. since you have to change the gear you should change the main shaft while you are at it. then you will know for sure if it is bent.

if it isnt bent,,[which it looks like to me] then you will have a spare which you will most likely need one day anyway.. jake.