I just completed the build on mine and it was straight as an arrow. There is a build thread a little furter down in the forum. It must be a defective elevator half. The dowel system works perfectly and there are no issues with it. It is plenty strong and rigid as designed. You can add a stiffner if you want to but its definitely not necessary. I have done some full throttle walls without a hint of a snap due to elevator flex.

I would contact Fliton and get another elevator/ or set of elevators. If its not built correctly I am assuming that they will probably ask you to send them back and they will send you another set.