Remove the cover from the top of the drive & look at the condition of the upper gearset. The u-joints look like the've been sitting in water, probably from a bad bellows which means you may also need a new gimbal bearing. If the gearset is shot you're going to have a hell of a time finding a mechanic who will do the work. Most guys won't work on OMC's. In that case it's either replace the drive with a used one or do the SEI/Merc conversion.
