Vintage Gruen Watch

I inherited this Gruen watch. In addition to what you see in the picture (Gruen_Marc.jpg):

- The back is silver in color, but I do not know its composition.

- The watch does not run. Rather, when I turn the crown, it sets the time, even if it is pushed in. When I pull it out, it clicks into place and still changes the time. When I push it back in, the return click is not as distinct.

I would like to sell this watch and will appreciate any information on its value.

Thank you.

Marc