I have a 1982 Mercruiser 470 motor/outdrive. Motor still runs great, but 2 weeks ago my prop spun out on me. The boat would still move at idle, so I purchased a rebuilt prop to get me trough the holiday weekend. Then, after launching, I never even made it out of the cove. The prop won't spin in neither forward or reverse. I checked the prop again today, and it doesn't appear burned out, and I can spin the shaft with the drive engaged. My question, is where do I start? I am a fairly experienced mechanic, but not so much with marine issues. Do I start with the lower unit, or just pull the whole outdrive? I'm headed to get a manual this evening, but I'm just hoping for some input on diagnosing the problem.