Meant to follow up on this...
The seller misrepresented the condition of its movement. He said it could use a service but didn’t say that the date wouldn’t change at all or that there was an obvious rattling of something loose inside. I debated reselling it with an honest appraisal of its condition, or fixing it. I decided to take it to a watchmaker I trust who is reasonably priced. He said a service will fix the date and he can source the part to fix the self-winding mechanism. $150 and and maybe I’ll get it back in 2017.
The exterior is in excellent condition and hopefully I’ll end up with a very nice watch and won’t have paid too much over value on it.
Lesson learned. $500 is my self-imposed limit on doing something impulsive and possibly dumb. I’m not made out of money, for sure, but I can eat a $500 mistake.