Blue? That is a real oldie. From the late 1980s. Likely 40-plus years old. IF the power head is really good, maybe repair the LU. If the power head has run in salt, or is in any way flawed, scrap the whole lot. A gasket set is available, and a COMPETENT mechanic can get the wp bolts out. Left twist drills are available, and well might get the snapped off bolts out. No blue LU's are available new now; they new ones will be "aquamarine" (midnight) blue, and will cost well in excess of $2K. Is it a 25 or 30" shaft length? A local scrap yard may have a suitable LU, but it would also need a new seal kit, wp kit, and so on.