Mission Building Tip
If you're building the Mission...one minor thing to look for. The instructions say to install the belt tensioner at its lowest point, then later install the motor mount to the chassis. When I did this the washer behind the nut on the belt tensioner prevented the motor mount from seating completely against the bottom chassis. (It may have seated if I had forced it by wrenching on the screws, but I prefer not to force it). This had the effect of tweaking the upper plate a slight bit.
When you install the motor mount to the chassis, loosen the belt tensioner a little before tightening the screws into the bottom of the motor mount. Check to make sure the motor mount is seated against the bottom chassis plate, then re-tighten the belt tensioner and keep going...
Hope this helps someone out there....