I had my furnace fixed recently - one of the things the crotchety repair-man did was force the vent damper open because the damper motor was shot. He didn't have another motor on him. He told me that the damper's only purpose was efficiency, but that it is very minor gain and I shouldn't even worry about it. I also got the sense that he was a guy for whom nothing good has been invented since 1975.
I needed the heat, so I let him go on his way.
Obviously I'm going to fix this thing eventually. But in your expert opinions, is this a big enough efficiency gain that I should get it fixed right away? If so, I'll do it. If not, I'll wait until the spring when I don't need the heat and try to do it myself, knowing I'm not going to freeze my pipes (or my family) if I screw something up