A rebuildable transmission core is expected to have problems, however, it must have a good cluster and a good case. A transmission that has been ran out of fluid to a point that it is locked up is not a rebuildable core. Also, if the transmission is already disassembled, it must be packed in a way that it is not damaged any more due to shipping. Furthermore, it must match the transmission or differential sent. If we send a Corvette T56, you cannot send back a T56 from a 4th Gen Camaro. If we send a 3 rib differential, you cannot send back a single rib differential, unless you have already paid for the upgraded case.