You said you limited it to shoulder height. Will it fly higher, or normal like it is supposed to?
The tail motor being notch isn't really a problem. My 230S has the same tail motor and it is notch also. It's not gonna be smooth like the main motor. Don't know why but that's how mine is.
A bent spindle will definitely cause the tail to twitch a bit. The easiest way to test for a bent spindle is to take one blade off, stretch out the other blade, then put an allen wrench or driver in to the empty blade grip, on to the spindle bolt or nut, whichever it has, then spin the bolt. If the stretched out blade wobbles at all then you definitely have a bent spindle. That can all be done without taking apart the whole head. If you do take the head apart, simply roll the spindle on something flat, such as a piece of glass and you can see if it is bent.