What threadlock did you use? I would recommend red or even epoxy to make sure the little bastard doesn't move. If the pinion gear shaft gets hot enough from heat transfer from the motor, it can cause the pinion gear to work itself free if the loctite is not strong enough. I had a similar issue awhile back, needless to say - I have increased the amount of loctite I use on parts now.
That being said, FCC will replace the part for you.
