4.3L OMC Cobra 1990. Had a leak at the transom so I pulled the drive. Found water in the bellows had rusted out the u-joint, gimbal bearing (it's frozen), yoke and part of the shaft. I can change the u-joint and gimbal. But, what else got damaged? Since the water got thru the bearing into the transom, I figure there's more damage somewhere. How tough a repair is this?