I think I might know what the problem is. However, without knowing if the person that originally put it together used all the right screws and parts in the right places, it may not matter.

When I first put mine together, I had a similar problem.

1. The first is the bottom plate (your pictures show this part?). There is a notch (possibly two) in it that matches a tab (again possibly two) on the upper hull.

2. The second, is on the gear ring. There is a tab with a nib on it, in the center of the ring. The nib should line up with with a notch in the base plate that it attaches to. Both the notch in step 1 and the tab described in this step will be on the same side.

The tabbed part of the assembly (from #2) will be on the forward side of the turret. There is also a molded rail on gear ring, on the same side as the tab, that trips the switch for the elevation limiter when it passes that area.

If those two parts aren't lined up, over time it's possible that the pressure from the screws, coupled with the mis aligned tabs and such, would warp the base plate. Once everything is lined up, the warping shouldn't matter, and might even straighten out some.