Sounds like you might have had the Gyro and tail working the right way around in the first place, then reversed them, then fixed the original problem (the drive gear rotating on the shaft). fix the shaft/gear problem (they should be fixed so you have no movement on from the gear to shaft.......they should move as one)then reverse th servo first (so it moves in the right direction, to move the tail/nose in the direction you want) then check the gyro, by moving the tail and seeing if it corrects in the right direction......then once all that is working, make sure you have plenty of head speed (tail speed) before applying pitch to the main rotor.
Don't give up. It can be frustrating (believe me, I know......I'm self taught and had no sim) but very rewarding when you get it right.
Cheers, Wiz.