I am looking to upgrade my combine. Currently I run about 250 acres a year and I have a NH TR70. I would like either a 1640 or 1660. I have heard from several people to stay away from the 1640 because they had transmission or final drive problems and share the drive parts with the 1620 and not the 1660/80, which makes them harder to find. Is there any other reason to stay away from a 1640 vs. a 1660? Other than production capability.