L/AF u33c's can be prone to the square shaft sliding out of its socket when the truck is pivoted far enough. The shaft either slides out unharmed and you need to pivot the truck back to that rotational extreme again and gently realign its flats with the walls of the socket, slip it back in and try to refrain from pivoting it that far again in the future. Or under certain conditions the shaft will break which means you need to replace it with the worm gear and shaft assemble GunRunner provided a photo of. Drop the power truck, one screw, you can leave the shell on. Be careful, the aft bearing can slide off and there's a very small, thin, clear washer behind it. Do not lose, misplace, or fail to have that tiny washer properly located when you install the new assembly. Another thing these engines are prone to is are misaligned truck rotational-limiting plastic plates. They are hot glued at the factory to the top side of the chassis (remove shell to view/access). Some were not correctly located when installed. One result can be unequal left-right degrees of truck rotation - it will swing further to one side than to the other. Be sure yours are allowing equal truck rotation/pivoting. If not, typically the side that is limited from rotating far enough can result in the engine derailing and/or a broken/sheared shaft when driven through a 20" (and especially <20") radius curve to that side - particularly at speed and/or pulling a significant load/train. The side that is allowed to rotate too far will often be the side from which the shaft pops out of its socket when the truck is rotated to its fullest extent.
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