First of all you have to realize that your terminology makes us think you are talking about the engine and not the unit, which can get very confusing. A good machine shop should be able to rebuild that shaft for you. Before taking it apart, show them your pics and ask them what they think. Probably cheaper than trying to find a new shaft. VERY, VERY, VERY, last resort you can permanently weld the flywheel to the shaft, but that will make any repairs down the road extremely difficult.