The Occam's Razor principle states that when there are two solutions to a problem the simplest one is the right one.Eight years and 12,000 rounds later is a fairly long period of time for a machining traced issue to show up.Odds on a new sear spring does it,I would also replace the safety because of the wear signs,however failing that I would then proceed to stake things on but then I would be staking new parts and not be out that much.