Meanwhile, set a large stockpot over medium-high heat. Add remaining 2 tablespoons grapeseed oil, and then onions. Sauté until soft, about 7 minutes, then add all remaining ingredients but the water. Continue to sauté, stirring often, until vegetables soften and wilt, about 10 minutes. Add roasted drumsticks, scraping any accumulated juices or brown bits in as well. Add the water. Bring mixture to a boil, then turn heat to medium-low (enough heat to produce a gently bubbling simmer). Add sea salt sparingly – just enough to bring out flavors. Cook until chicken meat falls off the bone, 2 to 3 hours.