You got a deal, for the price. You might get lucky, and just have a broke detent spring. Would not have required all the tearing down that you have done, but at least you are getting familiar with the bike, and working on it. Metal in the drained oil can mean all kinds of things, from nothing at all (some very small pieces of metal is almost normal depending on the miles) to something serious. If it were me, I think I'd just look for another complete engine, from a wrecked bike, ebay, craigslist, etc. Then you'll have all kinds of spare parts. Just ask questions here before you jump on something. This site is full of very knowledgeable people with lot's of experience on these bikes. And nobody will fault you for asking questions. The SEARCH function is your best friend.