Gruen Y.g.f. Tank Watch C. 1940

Details:

This is a vintage Gruen yellow gold filled men's watch, c.1940, with a 15 jewel mechanical movement. The crown is missing, but when I agitated the movement, it started to run. I don't work on watches, but even with my limited knowledge, I know this means there isn't anything major wrong with it. I can't wind it, and it's pretty well run down. This is a great watch for someone who does simple work on watches, my guess is a crown, a cleaning, and you'll be set....