The 518 weakness is the OD unit. Otherwise it's basicqally a rock-solid 727. I had to add a Transgo shift kit and a Transgo OD lube correction kit to mine. So far so good. The lube kit involved reaming the oil passage to the rear-bearing larger and boosting pump pressure. The shop that did mine gave up on the reaming after breaking a few DRILL BITS!!! I should have done it myslef!!! If I had it to do over, I'd keep the 727 and add a Gear Vendors OD unit!