Did they check to be sure the concave was level? I think they had a few get out that weren't level and needed worked on under warranty. I am pretty sure I remember the mechanic studying our latest machine very closely. We run the reverse bars. We have even added extras in some cases. They are helpful in some conditions and not as evil as many make them out to be. I always open the concave extra wide on corn and then close it in small increments until it is getting all the kernels off of the cob and grinding the cob as little as possible. This setting varies by corn variety and moisture levels. The new machines are more forgiving than our N5 was. It ground all the cobs no matter what you did, and then you sorted them out at the chaffer the best you could. When I looked over the fence at the neighbors corn stalks I would get "cob envy".