I would think that a used brooks would be a perfect fit... for the person that broke it in! I'm not sure why you would sell a used brooks unless it's sagging like a hammock - in that case, it's of no use to anyone.

Rain... if you can keep the bottom dry (fenders) then it should be fine. You will be sitting on top so that should keep it dry. If you are the type that gets out of the saddle, then you can buy a waterproof saddle cover (I have one- it works well) or you can use the plastic grocery bag. It hasn't been a problem for me - I commute in the rain sometimes five times a week.