Our apologize on not having the correct bearings in your kit. I do see that we shipped the correct ones on the 8th for you and they should have arrived on the 10th. If you have found a solution that works and no longer need the Dart, we do have a 30 day return policy that can be found here (https://www.andymark.com/returns.asp). Let us know if we can be of any further help.
After waiting for inventory to come back in, waiting for inventory to be released, waiting for it to ship out 4 days later and getting it just in time for our weekend long build thrash, we found out the DART, 12" Actuator Kit (am-3072a) was shipped with the incorrect bearings. This meant it could not be assembled correctly and no clear idea of how to modify it to work with what was provided. Needless to say Friday night I went home very depressed as the basic design of our robot depended on this product.
Lucky us, one of our engineering minded mentors woke up at 4 am with a brilliant idea and the robot design was saved. This means I now have a defective part that we no longer need and a big hole in my checkbook.