Just because it's old content doesn't mean that people won't help you clear it like normal. Remember that the Duty Finder matches you with randoms. Some people you match up with really just want the clear and don't care about helping. Some don't mind helping. The best thing you can do is use Party Finder and get friends and your Free Company to come help you clear. With Party Finder you can clearly state your goals so people who join know exactly what they are joining for.